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COOK/NG
UPA CIRCUIT?
Over EIGHTYRec1pes Inside:
see
Smart Dimmer
Auto Charger
Analogue Switches
63)
..:NEWS ....PROJECTS.... MICROPROCESSORS.... AUDIO..
.
FEATURE:Analogue Switching
PCB GUARD RING
TL081 OR CA3160 OR LF351
470n
NON -POLARISED
IN
II 4016
1
O OUT
d
HIGH = SAMPLE
LOW = HOLD
Fig.12b. A guard ring surrounding the capacitor can reduce leakage
across the PCB.
TL081 OR CA3160 OR LF351
PCB GUARD RING
IN/OUT
IN
,
L
T
BF244B
ó6 ó$
ó
O OUTPUT
ó ó ó
H
1N4148
HIGH
SAMPLE
LOW E HOLD
Fig.12a. Sample and Hold circuits.
I
Hold On To It
Sample and Hold circuits also employ analogue switches.
During the sample period, the storage capacitor is connected to the
input voltage via the switch which is turned on. When the switch is
turned off (Hold period) the voltage on the capacitor has got three
possible discharge routes.
1. As leakage across the printed circuit board. This can be greatly
reduced by provision of a guard -ring that surrounds the capacitor
with a potential exactly the same as that on the capacitor. Surface
leakage which is a function of potential difference is thus reduced
by removing the potential difference.
2. The switch can discharge the capacitor with leakage currents.
These are generally very small and insignificant.
3. The input bias current of the op -amp can discharge the capacitor,
but if a FET op amp is used this effect can be insignificant. If all three
discharge routes are small, then a long hold period can be
expected.
1---i
II
h
4
O-
B
4
BINARY
1OF8
3
O
COMMON
DECODER
OUT/IN
.INHQ-
4
4
More and Mode
The 4051 is an 8 way multiplexer (Fig. 13). This device has a 3
bit binary code input which it decodes internally to turn on one of
the eight analogue switches. The 4051 is effectively an 8 way single
pole, code selected switch. There is also an inhibit input; a logic 1 at
this pin turns off all the switches.
There are some problems to be encountered when using this
Fig.13. A 4051 analogue 8 -way multiplexer/demultiplexer.
OA
OB
CK
3Hz
OC
D
OUTPUT
VIN
RC
STOP
dt
DOWN
ADDRESS
INPUTS
TO
4051
4051
^^
^
20k
UP
--o
0
v v v
-0
UP DOWN
COUNTER
43"
30k
vvv
l
60k
(
--%V
RA
1
1
3
120k
VIN
100k
/WV
W
240k
O
Fig.11. A programmable integrator with reset to zero.
2
~^ Mn-i--g+
82k
ETI APRIL 1980
1+
OUTPUT
I
240k
W
I
'
l
'
5
7
+
(fTOTAL
CONTROL
RANGE 24de
11
II
INPUT
Q OUTPUT
Fig.14. An audio volume control with
3
dB steps.
21
device. The internal decoding exhibits some race conditions when
the input address changes which may cause switches to momenta-
Memory using a 4051 (Fig. 15). Analogue information is written
into memory by first selecting the address and then enabling the
'write' switch. The capacitor at this address is charged up to the
voltage level of the data in signal. Reading is performed continuously using a FET op amp so as not to discharge the storage capacitors.
This gives the RAM a tristate output capability, which when
used with the INH input allows several RAMs to be built
into a
larger memory system. Improved performance may be obtained
by
using 'break before make' multiplexers. An analogue RAM can be
used for producing short time delays and perhaps some rudimentary pitch shifting.
rily overlap in their ON states.
If the 4051 is used as demultiplexer with sample and hold
outputs, then the data on each output capacitor gets spread around
to other outputs during the overlap periods. This 'make before
break' effect can cause serious problems to occur. (There are )FET
'break before make' multiplexers but these tend to be rather
expensive).
Louder Yet
A programmable volume control can be constructed with a
4051 and an up down counter (Fig. 14). The state of the count at any
point in time determines which resistor is in the feedback loop of the
op amp. The resistors are arranged such that there is a 3dB change
in gain for each LSB change in the address code. By making the
counter count up the gain will increase and vice versa. It is necessary to stop the counter at 000 and 111 otherwise the gain will roll
round giving an abrupt change in level.
It is possible to construct an 8 bit analogue Random Access
STORAGE CAPACITORS
4051
I
LOW
HIGH
+
-
MPUs Get Theirs
Analogue switches are used in microprocessor data acquisition
systems (Fig. 16). An input multiplexer, addressed by the microprocessor selects which channel to look at. A sample and hold then
freezes the selected input signal so that the ADC can perform a
conversion on it. National Semiconductors make a single chip that
performs most of this data acquisition.
The chip, the ADC0817 has a 16 channel multiplexer, an ADC
TRISTATE OUTPUT
ON
o
/1III
O DATA OUT
Fig.15. (left). An 8 -bit analogue RAM using
4051.
a
TL081 OR CA3160 OR LF351
DATA IN
HIGH = WRITE
o-o
01
SIGNAL
INPUTS
O-
4051
2
a-3
a-4
OUTPUT
SAMPLE
AND
HOLD
O- 5
O-6
a-7
(right). A microprocessor data
acquisition system using analogue switches.
Fig.16.
ADC
DATA
MICROPROCESSOR
SAMPLE
A B C
I
f
ONE SAMPLE AND HOLD PER OUTPUT
COMMON
INPUT
MICROPROCESSOR
4051
0
DATA
-o
TYPICAL SAMPLE AND HOLD
I
Fig.17 (left). Analogue switches can also be
used in a microprocessor data distribution
system.
22
ETI APRIL 1980
FEATURE: Analogue Switching
tion (PAM). Sync pulses are mixed with this signal so that the
channels may be decoded at the receiver end.
Decoding is performed by stripping off the sync signal and
using it to address the demultiplexer. The required channel can
then be selected by monitoring the respective demultiplexer output
with a sample and hold followed by a 10 kHz lowpass filter. It is
important that the sampling frequency is at least twice the audio
bandwidth so that aliasing effects can be avoided.
and output latch, but you have to provide your own sample and
hold. Analogue switches are also used in microprocessor data
distribution systems (Fig. 17). Data generated by the microprocesor is converted into an analogue voltage by the DAC and is then
multiplexed into sample and hold circuits. This is a common technique for systems that require a large number of analogue parameters such as microprocessor controlled music and speech
synthesisers.
Mixing It In
Plexing Info
Monitoring the signal levels in an audio mixer can cause problems, due to the large number that have to be observed. There are
now several devices that use a conventional oscilloscope or TV to
display all the information on one screen (Fig. 19). Each audio
channel is processed by a peak detecting envelope follower. This
generates a signal that describes the peak signal amplitude in that
channel and it is known as a PPM (peak programme) response.
These PPM signals are then multiplexed and passed through a
single log compressor to give a display of level in dBs versus
the
In most telecommunication systems, a major cost is that of
informaof
channels
If
several
receiver.
to
transmitter
wire that links
tion can be transmitted down one wire then the cost of the overall
system may be considerably reduced. (Fig. 18).
example,
Eight audio channels, band limited to 10 kHz in this
is
channel
Each
multiplexer.
analogue
8
way
are fed into an
sampled every 50 nS for a duration of 6.25 nS. The eight audio
signals can thus be fed down one wire pair as a sequential series of
pulses that represent the instant values of the signals in the
eight channels. The process is known as Pulse Multitude Modula -
channel number on an XY screen.
ETI
CHANNEL
SELECTING
SWITCH
/SAMPLE
AND
(HOLD
8 WAY
10KHz LOWPASS
FILTER
MUX
i
Q
LARGE BANDWIDTH
DRIVER AMPLIFIER
A B C INH
8 AUDIO
RECEIVER
SIGNALS
(LIMITED TO
10KHz BAND
WIDTH)
SYNC
GENERATOR
The
Fig.18a.
receiver
used
in
OUTPUT
TRANSMISSION
CABLE
pulsed
a
SYNC
amplitude modulation (PAM) multiplexed
MULTIPLEXED AUDIO
SIGNALS + SYNC
8
sound system.
TRANSMITTER
CK 160KHz
Fig.18b.
The
multiplexed sound system
transmitter.
AUDIO
SIGNALS
FROM
MIXER
COMMON
OUTPUT
o
1
LOG
COMPRESSOR
4051
AUDIO LEVEL
DISPLAY
8
7
A B C
ENVELOPE
FOLLOWERS
(PEAK DETECTING)
tt
RAMP
1
GENERATOR
A
COUNTER
B C
Fig.19. (left). The levels of any number
of mixer channels can be displayed on
one screen with this multiplexed system.
ETI APRIL 1980
23
PROJECT
RADIO CONTROL
GUARDIAN
unit
A superb project for the radio control enthusiast. This unique
to
automatically sets as many as four servos or other control units
unit
pre-set 'safe' positions in the event of control -signal loss. The
control.
has four channels, each with fully independent fail-safe
Radio control fail-safe units are intend ed to be connected between the radio
control receiver/decoder and the sys-
tem's servóunits. Under normal operating
conditions the decoded command signals
pass straight through the fail-safe unit, enabling the servos to operate in the normal
manner. If, however, the command signals
are lost (because of a system failure or by
the receiver going out of range), the fail-safe
unit automatically feeds internally -generated pre-set command signals to the servos
and causes them to move to pre-set 'safe'
positions.
In a boat or a plane the fail-safe unit
may, for example, cut the speed and put the
craft into a gentle turn in the event of control failure, thus ensuring that the craft does
not simply disappear into the wild blue
yonder. In reality, only the most important
of the system's servos need to be subjected
to fail-safe control, so a four-channel failsafe unit is more that adequate for all practical applications.
Fail-safe units are already available
commercially but all of them suffer from a
number of defects. The Chromatronics
PP1 M-4CH is one example. This 4 -channel
unit measures only 41 mm x 62mm x 23mm
and is highly recommended for use in craft
with limited space and/or limited weight
carrying capacity. Specific defects of the
failPP1 M-4CH, however, are that it gives
safe operation only in the event of TOTAL
signal failure on all four channels and gives
no fail-safe operation if any one of the decoder output channels locks high. Also, all
the servos are pulsed simultaneously (rather that sequentially) in the fail-safe mode,
thus generating high (and possibly harmful)
transient currents in the system.
The ETI fail-safe unit described here
has been designed specifically as a 'De Luxe' unit that it gives a virtually fool -proof
performance. It is probably the most advanced fail-safe device ever published. It
has four FULLY INDEPENDENT channels,
each giving fail-safe operation if its own
lost or latches high.
The servos are pulsed sequentially (rather
that simultaneously) in the fail-safe mode,
decoder input signal
is
ensuring that excessive transient currents
are not generated in the system. Also, the
fail-safe frame width is adjustable, enabling
the unit to be used with electronic motor speed control units as well as with all types
of servo.
The performance sophistication of the
ETI fail-safe unit necessitates the use of a
total of six ICs in the design. The unit is in
fact built up on two PCBs which, when
stacked, give overall dimensions of about
52mm x 90mm x 25mm (uncased), making
it roughly twice the size of the Chromatronics PP1M-4CH. The unit is thus suitable
for use only in craft with a fairly substantial
amount of free space. The unit can be used
with any 3 to 9 volt positive -pulse radio
control receiver producing nominal pulse
widths of to 2 milliseconds (the 'standard'
range) and can control virtually all types of
1
3 -wire
servo.
Construction & Use
This is not a project for the beginner.
Construction calls for a good deal of care.
The first point to note is that one of the PCBs
is double sided, so unless you are really
good at making your own PCBs you'll have
to wait until ready-made boards become
available from one of our advertisers. Assuming that PCBs are available, doublecheck all their tracks to make sure there are
no breaks or shorts, particularly on the
double -sided unit.
Start construction with the double sided PCB. Use miniature components
throughout. Note that the three ICs are
CMOS types (normal 555s must NOT be
used in the IC5-1C6 positions) and should
be mounted in suitable sockets. If you have
a 'scope you can give the completed PCB a
functional check by connecting it to a 6 volt
battery supply and checking that pulses
with 1:3 mark/space ratios are available at
outputs R4-R8 -R12 -R16 and a variable 4 -
pulse train is available at the R17 output.
Construction of the double -sided PCB
calls for extra care. Veropins or similar
must be pushed through the board in various places (see overlay photos) and used
to connect the upper and lower tracks by
soldering to both sides of the PCB. Use
miniature components throughout the rest
of the assembly procedure, taking care to
observe the polarities of all devices. The
three CMOS ICs can be mounted in suitable sockets. When assembly is complete
decide on suitable casing arrangement (we
favour the idea of stacking the boards in a
home-made box) and then set about interconnecting the two PCBs. Seven interconnection leads are required and their positioning requires particular care, with constant reference to both the circuit diagram
and the overlay. There are two power supply interconnections and five interconnections to resistors 4-8-12-16 and 17.
When construction
is
complete, set
RV5 to mid position and give the circuit a
quick functional check by connecting a
servo and suitable supply to channel (A)
1
output and check that the servo position
can be varied via RV1. If all is well, recheck
the servo functioning on channels 2 (B), 3
(C) and 4 (D), using RV2, 3 and 4 respectively to give control.
The procedure for fitting the completed unit into an installation is quite simple.
The unit connects between the receiver/
decoder outputs and the servo inputs.
When installation is complete switch the
receiver on and the transmitter off and adjust the fail-safe unit's pre-sets to set the
servos to the desired fail-safe positions. Finally, switch on the transmitter and confirm
that the system responds to normal remote
control and reverts to fail-safe when control
is
removed.
BUYLINES
All components used in the R/C Fail -Safe
unit should be readily available from major
stockists.
29
ETI APRIL 1980
21
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DESIGNER'S
NOTEBOOK
In this month's 'Notebook' project editor Ray Marston takes
a peek at the fascinating world of 'touch switch' technology.
f you ever get involved in the design of electronic equipment,
there is a fair chance that you will eventually come accross a
circuit that requires the use of a 'press-to -do -something' switch.
You'll then have to decide whether to use an electro-mechanical
push-button switch or a solid-state 'touch' switch to do the job.
The main disadvantages of the push-button switch are that it is
a bit expensive and is available only in those
designs that manufacturers care to produce. These switches are also
'noisy' in that they generate contact-bounce spikes that can play
havoc with fast digital circuitry.
This last mentioned problem can be overcome by using the
'debouncer' circuit of Fig 1. Here, one quarter of a 4093B CMOS
quad 2 -input NAND Schmitt is used as a simple Schmitt trigger.
When PBl s closed, Cl charges rapidly to full supply volts and the
Schmitt output switches high: When PB1 is released Cl discharges
slowly via Rl until eventually the Schmitt output switches low.
again. The circuit is thus unaffected by switch contact bounce and
produces a clean on/off signal at the Schmitt output.
unreliable, tends to be
Touch Switch Circuits
The main advantages of solid-state switches are that they are
reliable (they have no troublesome mechanical parts), can be less
expensive than their electro -mechanical counterparts and can
readily be produced in almost any shape or form that the designer or
home constructor wishes.
Touch switch circuits come in three basic types (ignoring
'freak' circuits such as thermo-switches, etc). The crudest and least
attractive of these are the 'resistive' types, which use the 'touched'
or 'untouched' resistance change that occurs between two adjacent
touch contacts to give activation.
5 TO 15V +Ve
OUT
Y.
40938
TOUCH
CONTACTS
5 TO 15V .1-Ve
uV
Fig.3. Resistive touch switch.
Fig. 3 shows a typical resistive touch switch circuit. Normally,
with the contacts untouched, Rl holds the Schmitt input high and
its output is low. When a finger is used to bridge the two contacts
Fig.1. Push-button debouncer circuit.
the resulting skin resistance (less than 3MO) pulls the Schmitt input
low and drives its output high. Cl is used to 'debounce' the circuit.
Fig. 4 shows how the circuit can be modified to give 'toggle' action.
Fig. 2 shows a useful way of obtaining a toggle (alternate on off) action from a simple push-button switch. The switch signal is
debounced by R1 -C1 and is then used to clock one half of the
40278 dual JK flip-flop, which divides the clock signal by two.
Thus, the 4027B output goes high on one press, low on the next,
high on the next and so on. Two of these toggle switches can be
built from each 4027B IC.
F.
TO 16V +Ve
Fig.4. Resistive touch toggle switch.
Fig.2. Push-button toggle switch.
34
A very serious disadvantage of the resistive touch switch is that
it can be disabled by moisture or contamination bridging the contacts. Also, it may be disabled by persons with damp fingers or may
be immune to operations by persons with very dry skins.
A great improvement in reliability is given by a second type of
'hum detecting' touch switch. This type of circuit relies for its
operation on the fact that the human body acts as a kind of antenna
ETI APRIL 1980
FEATURE
TOUCH/PROXIMITY
'CONTACT'
5 TO 12V +Ve
+12V
Cl
TOUCH
CONTACT
98
1n0
R2
44,7
OUT
47
'/.40939
OUT
BC109
40930
1
L1
154148
01
OC109
1mH
R1
154148
03
BC109
10M
RV1
OV(EARTH)
5k0
SENSITIVITY
154148
Fig.5. Hum -detecting touch switch.
OV(EARTH)
Fig.8. Damped oscillator touch/proximity switch.
that is coupled to the mains and carries a high -impedance mains
signal. Fig. 5 shows an example of this type of circuit. When the
input contact is touched the hum pick-up signal is fed to the input of
the first Schmitt stage via limiting resistor R2 and produces a full amplitude square wave at the Schmitt output. This square wave is
converted to DC and debounced by the D1 -R3 -R4 -C1 network and
drives the final output of the second Schmitt high. The Schmitt
output goes low again some 60 mS after the input touch is removed.
Fig. 6 shows how the above circuit can be modified to give toggle
operation: D2 and C2 prevent unwanted feedback from the 4027B
to the Schmitt.
+
5
C3
100n
10C1
0n
6110 11116
R3
TOUCH
CONTACT
56k
R2
4027
47k
á4093E1
7N4148
C2
1n0
Fig.6. Hum -detecting touch toggle switch.
B
ing of oscillator harmonics. Of particular interest is Fig. 7d, which
shows that these effects can be obtained without physical contact,
by capacitive or 'proximity' coupling.
Fig. 8 shows the practical circuit of a touch/proximity switch
that works on the oscillator damping principle. The oscillator is a
Colpitts, working at about 300 kHz. RV1 is carefully adjusted so
that oscillation is barely sustained when the contact is untouched.
Under this condition the rectified output of the oscillator drives Q3
to saturation and holds the circuit's output low. When the contact is
touched the resulting capacitive loading kills the oscillator, causing
Q3 to turn off and switch the output high. The output has relatively
slow rise and fall times, but can be speeded up with a Schmitt circuit
TO 12V +Ve
if required.
The zero volts line of the Fig. 8 circuit should (ideally) be
OUT grounded. The touch contact must be made from a conductive
material, but can be any shape or size that is desired: in most cases
the 'contact' face can be covered with an insulating material withOVIEARTHI
out detracting from the circuit's performance. Pin -head sized contacts will require actual -contact operation, but 'contacts' with surface area of a square metre or so can be proximity -operated at
ranges up to 20 - 40 cms.
Capacitive
NOTE;
IC1 IS 40016
Touch/Proximity Switches
The third and most important class of switch are those that
work on the capacitive loading principle. In most simple cases,
these circuits rely on the fact that the human body acts as a small
capacitor that is earthed at one end. The actual value of capacitance
depends on physique and on environmental conditions, but is
reckoned to have a value of 150 - 300 p under normal domestic/
industrial conditions.
Fig. 7 shows a number of basic ways of using the body capacitance effect. In Fig. 7a it causes loading of an HF oscillator, in Fig. 7b
it causes capacitive potential -division and in Fig. 7c it causes filter -
MAN
weleee
200pF
SERIES
RESISTOR
/
PROXIMITY
PLATE
OUT
1-50
!MAN
(c)
-200p
-
MAN
2000
Id)
Fig.7. Body capacitance effects on a touch contact. (a) Causes oscillator
loading, (b) capacitive potential divider action or (c) degradation of
oscillator waveform (harmonic filtering). (d) If contact is of sufficient
area, loading and other effects can be obtained without physical contact, by capacitive or proximity coupling.
ETI APRIL 1980
o
+12V
C2
(REGULATED)
47p
'TOUCH'
CONTACT
V71C1
470p
N
OUT
02
1N4148
40278
RV1
10k
SET
LEVEL
01
1N4148
C3
100n
R4
1k0
OV
(EARTH)
Fig.9. Capacitive -divider touch switch (left) with modification for
toggle operation (right).
Finally, Fig. 9 shows the circuit of a touch switch that works on
the capacitive -divider principle. Here, IC1 is wired as a ring -ofthree oscillator working at a frequency of a few hundred kHz. The
oscillator output is fed to a capacitive potential divider formed by
C2 and the stray capacitance around D1 and the touch contact. The
resulting potential divider output signal is rectified by D1 -D2 -C3 R2 and fed to the 3140 regenerative voltage comparator, which is
adjusted (via RV1) so that its output is just switched to the low state
when the input contact is untouched. When the contact is touched,
the resulting capacitive loading increases the effective capacitance
of the lower half of the potential divider, thereby reducing the
divider's output voltage and causing the 3140 output to switch
high. Fig. 9b shows an add-on section that can be used to convert
the circuit to toggle operation
As in the case of the Fig. 8 circuit, the zero volt line of Fig. 9
should be grounded. The touch contacts can again be any desired
shape or size.
ETI
35
PROJECT
AUTOMATIC
BATTERY CHARGER
A 12 volt battery charger
project that automatically
switches to a 'trickle
charge' mode when the
battery reaches full
charge. The circuit can be
built as a stand -alone
project or can be used
to up -date an existing
charger.
Conventional car battery chargers are
simple and inexpensive devices
which continuously charge the battery (at a rate of a few amps) for the duration
of the switch -on period. The owner has to
occasionally check the state of the battery
with a hydrometer and switch the charger
off when the battery reaches the 'fully
charged' state. If the owner does not switch
the charger off the battery will overcharge
and its electrolytic solution may eventually
be lost through evaporation or the cell
plates may buckle and destroy the battery.
Our ETI battery charger overcomes the
deficiencies outlined above. It incorporates
an electronic charge -state sensing and
feedback control network which causes the
battery to charge at maximum rate until
full -charge is attained, at which point the
charger automatically switches to 'trickle
charge' mode which maintains the battery
in the fully charged state indefinitely. A red
LED illuminates when the battery is fully
charged.
Our charger is designed to charge 12
volt batteries only. The unit can either be
built as a self-contained 'stand-alone' project, complete with transformer and case,
ETI APRIL 1980
etc, or alternatively the electronics can
simply be added to an existing charger unit,
to update a conventional design. We have
included the circuit of a typical 'conventional' charger, for comparison purposes.
Construction & Use
Construction of the unit should present
few problems. If you decide to build the
complete 'stand alone' project, assemble
the PCB components exactly as shown in
our overlay, noting that the two LEDs are
mounted off-board. If you decide not to fit
the optional meter (a difficult -to -get component, which MAY be available from
some car accessory shops) short the two
M1 connections together using heavy
gauge wire.
If you decide to simply use the automatic charger circuit to update an existing battery charger, omit BR1 from the PCB and
take the outputs of your existing charger
rectifier directly to the appropriate '+' and
points on the PCB track. Whichever
version of the unit you decide to use , be
sure to use a reasonably heavy gauge of
wire for the main interconnections.
-'
When construction
RV1 slider fully
is
complete, turn
tothe'ground' position and
give the unit a functional check as follows.
1 Check that, with no battery connected,
both LEDs illuminate.
2 Connect a car battery into place on the
charger. Check that LED No. 2 turns off and
that a charge current (typically 2 to 4 amps)
flows to the battery.
3 Rotate RV1 and check that LED No.2 can
be turned on and the charge current cut off
via the pot.
4 Return RV1 slider to the 'ground' position
and charge the battery up using the normal
'hydrometer' technique. When the battery
reaches full charge, carefully adjust RV1 so
that LED No. 2 just starts to turn on and the
charge current falls to a 'trickle' level of a
few hundred milliamps.
If RV1 is correctly set, you'll find that
on subsequent charges LED 2 will first start
to flicker as the 'full charge' level is attained. The LED will subsequently turn on at
reduced brightness or will alternatively cut
on and off as the 'fully charged' state is
maintained. RV1 should require no further
adjustment throughout the life of the
charger.
39
r
T1
L
FS1
NOTES:
5A
SCR
1
IS
BTY 79 OR SIMILAR
GREATER SCR
6 AMP OR
SCR 2 IS C106D
D1 IS 1N4001
17V
4A
BR1
MAINS
INPUT
50V
6A
015AMP
(ON HEAT-
N
SINK
LED 2
CHARGED
OPTIONAL
METER
I
470R
LED
ON/OFFr.,
SCR
1
C
Circuit diagram
battery charger.
Fig.1.
R4
1k2
D1
of the automatic
ZD1
6V8
R1
12V
BATTERY
T
ON CHARGE
L
SCR 2
G
470R
(right). For comparison we have
included the circuit diagram of a conventional charger.
R3
470R
HEAT
SINK
1
I
141
RV1
Cl
100u
25V
4k7
SET
CUT-OFF
LEVEL
R5
10k
O
Fig.2.
MAINS
INPUT
0-5A
MOVING IRON
RV1
1R0
(OPTIONAL)
(Below). The PCB and transformer installed
in a suitable case. Note the heatsink on
SCR1.
T
12v
BATTERY
ON CHARGE
K
a
Fig.3. Connections to SC R1, the BTY79.
40
ETI APRIL 1980
FEATURES
DIGEST
ANALOGUE SWITCHES
DESIGNERS NOTEBOOK
AUDIOPHILE
CIRCUIT SUPPLEMENT
MICROFILE
RAVEN ON
9
....And
now the good news
18 Taming analogue signals
34 Touching technology
44 Sounds peculiar
55 16 pages of goodies
82 New machines on view
92 Chinese style
TOMORROW'S OFFICE 96 Crystal balls at the ready
TECH TIPS 103 More of your ideas
A complete budget system p.44
PROJECTS
RADIO CONTROL FAIL-SAFE 28 A DIY guardian
BATTERY CHARGER
CAR SECURITY DEVICE
300W AMPLIFIER MODULE
TOUCH DIMMER
Protect your motor p.50
+68V
C3
2500
0v
_
C2
2500
T
Circuit
supplement
:_
..
T'
C4
.drma M
-
39
50
74
87
INFORMATION
ETI MAY
MARKETPLACE
17 It certainly will
37 Your bargain basement
SPECIALS 54
ETI PRINTS 81
CT MAY 95
ETI 1999 101
BOOK SERVICE 109
p.55
A phone with
a difference p.80
angel
Automatic charging
Alarming possibilities
More power to your elbow
The dimmer with a difference
A few extra this month
Rub down a PCB
The Hobby future
A very SPECIAL special
Technical tomes
EDITORIAL AND ADVERTISEMENT OFFICE
145 Charing Cross Road, London WC2H OEE. Telephone 01.437 1002/3/4/5
an.Sc.
on
Ron Harris B.Sc.
OVERSEAS
EDITIONS
AUSTRALIA
:
M. RB
IDiegoaham
Dee Camilleri, Enzo Grando,
Loraine Radmore, Lorraine Stout
Paul Edwards, Tony Strakas,
Roger Harrison
Editor
CANADA
.
GERMANY
:
HOLLAND
esston
Joanne
Ray Marston
Keith Brindley, John Fitzgerald
Steve Ramsahadeo
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T.J. Connell
Halvor Moorshead
Editor
Udo Wittig
Editor
Anton Kriegsman
$
Editor
PUBLISHED BY
DISTRIBUTED BY
V
PRINTED BY
MODMAGS LTD
Electronics Today International
©COPYRIGHT: All material
accuracy but ETI cannot
ETI APRIL 1980
is
is
Editor
Assistant
Edr itor
Art Direct
Production
Technical Illustrators
Project Editor
Project Engineers
Project Development
Advertisement Manager
Advertisement Production
Advertisement Representative
Managing Director
Modmags Ltd., 145 Charing Cross Road
Argus Distribution Ltd. (British Isles)
Gordon & Gotch Ltd. (Overseas)
QB Limited, Colchester
normally published on the first Friday of the month prior to the cover date.
subject to worldwide Copyright protection. All reasonable care is taken in the preparation of the magazine to ensure
for it legally. Where errors do occur a correction will be published as soon as possible afterwards.
be held responsible
3
PROJECT: Battery Charger
HOW IT WORKS
T1
is usually sufficient to limit
the charge current to a safe value: 'De.
Luxe' battery charger sometimes have a
low -value rheostat in the series network,
enabling the charge rate to be varied over
T1
VIA
FS1
In a conventional battery charger (see diagram) the unsmoothed full -wave rectified
output of a 17 volt transformer is fed to
the battery via a moving -iron 0-5A monitor
meter. The battery is charged by a 'pulsed'
current at a rate determined by the differential voltage between the battery and the
charger and by the total series resistance of
the circuit (the effective resistance of the
transformer, rectifier, meter and battery).
A 'flat' battery has a low terminal voltage
and typically draws an initial charging
current of about 4 amps, falling to about
2 amps as the terminal voltage rises to the
full charge value. The total series resistance
of the circuit
limited range.
You'll notice from the above description that the battery terminal voltage rises
as the battery charges up and can thus be
used to give an indication of the state of
charge of the battery. This fact is put to
a
practical use in our automatic
charger, which operates as follows.
M1
LED
-ve
2
LED2K
LED1
K
battery
Silicon controlled rectifier SCR1 is
wired in series with the battery circuit and
can be gated on via the R2-R3-LED 2
network: this network can be disabled by
gating on SCR2. The battery terminal
voltage is monitored by the R4--C1-RV1ZD1 network and turns SCR2 on when the
terminal voltage exceeds a value pre-set by
RV1.
When a 'flat' battery is first put on
charge its terminal voltage is low. Under
this condition SCR2 is cut off and SCR1 is
gated on in each half cycle via the R2-R3LED 2 network. SCR1 acts as a simple
rectifier under this condition wand the
battery charges at maximum rate: the forward volt drop of SCR1 is only a few
hundred millivolts and is insufficient to turn
LED 2 on.
As the battery charges up its terminal
voltage rises. If the terminal voltage rises
above the trip level pre-set by RV1, SCR2
is gated on via ZD1. Under this condition
SCR2 removes the gate drive from SCR1,
which turns off and no longer passes a
charge current to the battery: LED 2 is
turned on via SCR2 and R3, indicating that
the battery is fully charged.
In practice, the terminal voltage of the
battery depends on both the battery state
and the magnitude of the charging current
and decreases when the charging current is
removed. Consequently, the circuit does not
abruptly stop providing a charging current
when the battery reaches full charge, but
goes into a progressive skip -cycling mode,
which progressively reduces the mean
charging current to a low 'trickle' value.
This action automatically maintains the
battery in a fully charged (but not overcharged) state.
The correct setting of pre-set pot RV1
is established initially by charging the
battery up in the conventional (hydrometer,
etc) manner until it reaches the fully charged state. RV1 is then carefully set so that
the charger goes into a skip -cycling or
trickle -charge mode under this condition.
The RV1 setting is then valid for all subsequent 'automatic' recharging actions.
Current monitor meter M1 is an entirely
optional component in this circuit.
ETI APRIL 1980
LEDI
+ve
Ml
PARTS LIST
Fig.3. Component overlay. Short the meter
connections together with heavy gauge
wire, if you decide not to fit the meter.
RESISTORS :
470R
R1,2,3
R4
1k2
10k
R5
POTENTIOMETERS
RV1
:
4k7 preset
CAPACITORS
100u 25V electrolytic
Cl
SEMICONDUCTORS
:
SCR1
8TY79
SCR2
C106D
1N4001
ZD1
6V8 400 mW
TIL220
200V @ 6A
Dl
LED1,2
BRi
MISCELLANEOUS:
Charger transformer CT4, 5A fuse, dPdT
Toggle, instrument case, H 95, W 125,
D
220mm.
ETI
BUYLINES
All components used in the Battery Charger
are available from major stockists. The
Charger transformer can be obtained from
ElectroValue.
41
AUDIOPHILE
Ron Harris goes gardening with some rogue speaker
boxes and shifts his sights to budget hi-fi.
Around the middle of this month I got lost. Nothing unusual in
that, you may say, some of the best people get lost from time
to time. This was in the country though, surrounded by all
these woolly pre -packed lamb chops and things. Healthy things
too, like fresh air, grass and circular brown patches of earth that
heave up and drown your shoes when you step in them...
Being of sound mind and thirst, the first thing I do when lost is
head for a pub. One of Britain's real strong points that is, regardless
of where you are or who you are, you're never more than half-an hour from a pint of bitter and a barmaid.
Sure enough after about ten minutes of 40 MPH down these
'roads' a suitably shaped building loomed in the headlights. All
would be well now, with a pint inside us and some worldly words of
wisdom from the friendly landlord we'd soon be heading back into
civilisation.
Oh yeah?
This pub turned out to be the one Hammer films line up
werewolves outside for howling practise. Weird it was, surrounded
by a massive car park which was totally devoid of cars. Just the wind
and us.
Once inside suppose it wasn't that bad, empty but not bad.
The only customer was the 'local character', otherwise known
as
the tramp, a little lumpy old man whose party trick turned out to
be
saying 'Hello Sailor' in ten languages. Probably explains the lumps.
Stranger yet was the manner in which music issued forth into
the
bar. Had they been playing church organ or choir stuff I'd had been
across those fields faster than the Russians in Afghanistan.
No speakers you see. A nice plain ordinari' music centre, being
played by a nice plain ordinary barmaid and nice plain ordinary
music, but no speakers. We searched the place, - plenty of pretty
beams and dead animals around the walls, but no speakers. Upon
enquiring at the bar was informed by a suspicious look, a grunt and
a wave which took in half the known Universe, that they were 'over
there'.
Not wishing to look too ridiculous, looked around again.
Slowly it dawned that the only things in approximate position to be
producing sound were two massive cylinders covered in greengrocers grass! From zero feet away it became clear that was indeed
the source of the treble -less thudding which prevaded the building.
I
I
I
Green Green Grass of Ohm
Oh my God! A closer look into these apparitions acquired
overwhelming importance. 'In the name of Audiophile, command
thee - revelest unto me thine drive units
' sort of thing.
Anyway, while our illustrious Art Director distracted the barmaid - a brilliant tactical maneouvre involving a pint glass,
the
tramp and two felt tip pens - managed to peel back the turf a little.
I
I
Inside resided three KEF B200s and a T27, no crossover,
and no
padding. The tweeter pointed up out of the top of the cylinder while
the mid -ranges units attempted to push the rest of the sound straight
through the grass, failing miserably.
A great deal of work hid obviously gone into the construction
of these enclosures and no doubt someone somewhere thought that
grass finish attractive. The end result was nothing short of an horrific
treble free thudding which occasionally coincided with the music.
As I've no idea where the pub is, short of saying it's somewhere
north of London but south of Colchester, at least ain't gotta go back
and be thudded at.
I
If there's a moral to this tale at all it must be to avoid home-
brew speakers, even in pubs.
Budget Time
Three hundred pounds is not a lot' by today's standards.
Right now it buys you 1/2oz of gold, or maybe the rear bumper of a
new car. Once upon a time (of inflation) it would have bought you a
very nice little hi-fi too, although to-day around five hundred is
more like an average starting price.
However, the arrival at ETI of a JVC amplifier, the AS5, with a
retailing price of around £85 and a nice sound indeed provoked some debate as to how possible it is to assemble a complete
(record playing) system of good quality for that £300
That then, is the starting point for the system described here. All
in all, at present prices, the outfit totals between £293 and £327
depending on the state of your discounts.
Giving names to it all produces a list which looks a little like: TURNTABLE: JVC QLA5R
- quartz lock, auto return. Wow/flutter
0.04% DIN. s/n 75dB DIN.
CARTRIDGE: CORAL 555E - elliptical stylus. Compliance =15/20 cu. FR. 20-20k = 2dB. output 4mV (5 cm/sec
Ik).
AMPLIFIER:
JVC AS5 - 30W rms at 0.06% the across 20-20 kHz
phono:- 2mV/47k, overload 150mV, s/n 70dB.
SPEAKERS:
VIDEOTONE GB2 - 50W (RMS) power holding,
two unit ported design.
OK, so I know that there is nothing British in there and that the
Goldring G900E and any one of several British loudspeaker manufacturers have good reason to feel left out, but then most
of those
products have been reviewed to death elsewhere and the components employed here all have a great deal to offer in their
own right.
So no Union Jacks in the post, eh? (I've got
one anyway!)
Photographs of Felicity Kendal are of course perfectly acceptable
Around a Roundtable
The turntable, JVC, QLA5R, is fairly new and retails
at the
£100 mark. For that you acquire an auto -return quartz -lock machine with a good (but flimsy) construction and the possibility
of
varying the speed, should you so desire, by ± 6%. Quaintly
entitled
a pitch control, this facility is even endowed with
some nice little
lights to show how far away from the correct speed you
are.
All these speed change facilities have one thing in common
they are totally and utterly useless. Better to have
spent the pounds
on a more solid plinth. A turntable that goes around
at 29 or 37 RPM
is wrong, whether by design or not.
44
ETI APRIL 1980
NEWS
Right: the JVC QLA5R turntable. As you
can see the finish is to a very high standard
and good adjustment is provided on the pickup
arm. Noise level from the deck was around the -45
dB mark under test and no meaningful comment could
except that
be made about the quartz- lock speed control
is is accurate! Experiments seemed to suggest that this deck
is a good partner for low compliance moving coil cartridges.
-
Below right:the Coral 555-E installed in the deck. Its
depth necessitated raising the arm pillar an appreciable
amount, which the deck could cope with, but the instruction
book couldn't! A good cartridge and excellent value for money.
The arm is of a good standard with high quality bearings and a
nice range of adjustments - unusual on an automatic in this league.
The turntable switches on as you move the arm from the rest, and is
turned off once the arm returns, its duty done.
The strobe markings around the rim are machined into the
platter itself and, having sharp edges, are the best reason you'll find
for not touching the deck until itjas stopped! (I've got the scars to
prove it, too).
At first was less than happy with the deck - the lift/lower
behaved like a Kamakaze pilot for a start - and I thought the plinth
too light. However, once you have adjusted the arm height for a
good clearance, totally ignoring the misleading instruction manual,
the lower control performs more sensibly. The deck is certainly
more prone to acoustic feedback than might like, but a good solid
mounting shelf (no coffee tables entertained) should prevent any
trouble there.
I
I
Getting the Point
My cartridge, is from the same stable as the amazing MC81
(which remains my nomination for God's gift to hi-fi) and all sarcastic cries of 'surprise 'surprise' will be studiously ignored. The Coral
555E is a moving magnet design o. more restrained ambition and
hence more general appeal. At its price of somewhere beneath £20
it faces numerous competitors of varying ability, so there is no lack
of units to compare it against!
Physically the 555 is quite a deep unit with a medium/low
compliance rating, and a weight of six grammes. Output is high-ish
at around 5mV at 5cm/sec, and so an amplifier with a healthy
overload is called for, lest it clips away at the peaks other beers can't
refresh.
Once the arm height had been suitably adjusted the Coral
proved a good match for the QLA5R and gave a satisfyingly musical
reproduction in the test system. Substituting the deck into our
reference system could only be called unfair suppose, but still it's a
cruel world anyway so what the hell...
I
ETI APRIL 1980
The deck itself is a competent offering, very good mechanically
and producing a good sound quality at its price. Compared against
a high quality reference the sound is shown to be a little boomy,
probably due to its constructional failings. A slight edge is imparted
to the higher regions too.
However, being unfair has the advantage that once you start
you may as well carry on, so took the 555E out of the QLA5R and
the reference MC81 was parted from its carressing SME 111 and the
two interchanged. The JVC handled the moving coil unit very well
indeed and the results were very, very impressive.
The 555 in its turn was shown to be a high class unit by
absolute standards, lacking only that subtle handling of complex
signals which comes only with a high pile of poundnotes. Tracking
is competent, if not outstanding, and the sound balance is a well
restrained mixture on the right side of bright - if you'll pardon the
rhyme.
I
45
Centre Point?
And so to that from where we came. JVC's A -S5 began this and
indeed a worthy offering. As you can see from the photo it has a
simple appearance (if I was polite I could call it restrained) but it is in
full possession of all necessary controls. The tone controls are of the
'click' variety and worked well in use producing no deterioration in the quality of sound for a moderate amount of tonal
correction.
Although 30W is not a great deal of power by today's standards, the JVC performed well in most situations. A large room with
large speakers is not the universe in which this star shines brightest,
nor is it intended to do so. When used sensibly the A -S5 has a clean
sound with -good smooth treble extension and a firm bass response.
With speakers of the ABR type i.e. Celestion 15's etc. a certain lack
of control was noted, which vanished with infinite baffle or ported
speakers such as the Videotone GB2s married to it here.
There is nothing in the specification to explain this oddity. The
is
damping factor holds up well at all frequencies - which is the
first place one searches in a case like this. Anyway, a minor condition, a trifle in fact. Choose your speakers well and enjoy the best
amplifier sound available under £100. All comes included!
Congrats JVC.
Point of Speech
Hands up all those who have not heard of the Minimax.
No takers?... One?... Who? Never heard of him either.
Oh very well
they were the greatest thing since ears a few
years back, sweeping all before their cones - including the reviewers. Singlehandedly they... etc... etc... etc... That's right, a past rave
machine. Correctly so, at the time. Videotone established themselves in the UK with the Minimax's and have consolidated since.
The GB2 is a well made little two unit enclosure of ported
intent and a hefty bass punch for its size. It matches the A -S5 very
well and for its £100 asking price returns a good deal of perfor-
Right:
a naked GB2.
The port is visible
below the bass unit in
the photograph. The
bass
unit itself seems
small for the enclosure
size at first but gives a
good account of itself.
The only criticism
had of the speakers was
that they were more
directional than most
enclosures with a dome
HF unit. Perhaps that
(relatively) wide baffle
A metal tape. Anyone who has tried to buy one of these
elusive plastic cases will no doubt appreciate the sight.
Machines to play the metallic illusions DO exist however
and next month I'll be revealing the ferric truth about the
£200 example of the iron art.
Sony TCK 55 II
The cassette? Oh, well that is because Sony are shipping them in quantity which means that TDK no longer
have it all their own way.
-
-a
had something to do
with it. Overall though
the GB2 is a fine little
speaker which will take
a bit of power and
return a healthy bass
punch.
46
ETI APRIL 1980
NEWS:Audiophile
Left and Far Left the
machine which is to blame
for this months Audiophile,
AS5 from VC. As you can see
from the internal shot the amp
is very well made with sensible
heatsinking. I hasten to add
that the tone control settings
shown were put on by our
photographer and NOT by me.
He even managed to press the
before I
loudness button in
decapitated him for sacrilege.
I tried hard to find something
wrong with this amp and was
sorely disappointed! Highly
highly recommended.
:
J
-
mance. The overall sound is smooth., with a slightly recessed midrange and may be a little lacking in that presence so beloved of
hard -rock enthusiasts. Nonetheless, the compromise is a good one
at this price level and one which will tune many a phono
cartridge. A good match here for the Coral 555E, lending a balanced and well extended sound to the system overall.
So there you have it. A £300 system of fine pedigree and
performance. It will not fill the Albert Hall with 100 dB of suicide
watts, nor will it rattle the neighbour's china from his mantlepiece.
It will provide a good accurate rendition of vinyl information
presented to it in the average living room, however, and that is all
you could ask in a system - is it not?
No?
ETI
-
Why not?
FASTER THAN A SCOPE
.SAFER THAN A VOLTMETER
LOGIC MONITOR
LM -1
Instant - simultaneous
monitoring of the logic state
IC nodes
allit over
of clip
your IC.
Just
LM -1 Instantly and accurately shows both static
and dynamic logic states on a bright 16 LED
display.
LM -1 finds its own power.
LM -1 cuts out guesswork, saves time, and eliminates
the risk of short circuits.
LM -1 is suitable for all dual -in -line logic ICs.
LED on = logic state 1 (high), LED off = logic state
0 (low), and each LED is clearly numbered 1 to 16
in the conventional IC pattern.
ONLY £48.70
plus 15% VAT, plus post and packing
Total £34.44 including box and
instruction manual.
CONTINENTAL
SPECIALTIES CORPORATION
C.S.C. (UK) Limited
Dept. 9S2, Unit 1, Shire Hill Industrial Estate
Saffron Walden, Essex. CB11 3AQ
Telephone: Saffron Walden (0799) 21682
Telex: 817477
ETI APRIL 1980
----
I
I
I
I
=MI=am elm _®mi
CONTINENTAL SPECIALTIES COPORATION DEPT. 9S2
Unit 1, Shire Hill Industrial Estate, Saffron Walden, Essex.
Name
Address
QUANTITY
REQUIRED
LM1. £34.44
FREE catalogue
Tick box
enclose cheque/PO for
I
inc. p & p and VAT
Phone your order with Access, Barclaycard or American Express
Expiry date
LCard No
I
I
I
I
_I_®____®®®®
47
CAR SECURITY
DEVICE
Bring your ETI Car Alarm up to date with this add-on alarm control module
from Compu-Tech Systems. This module's muscle is guaranteed to double
your alarm's scare coefficient.
any readers who have built and
installed the Compu-Tech Systems
car alarm (featured in ETI, December 1978) have expressed an interest in two
additions to the alarm system, which increase its effectiveness at night and in noisy
or high theft risk areas. This unit is also
recommended if your horn is prone to
faults or if it is located in an easily accessible place. If it's easy for you to get at, it's
equally easy for a thief to get at.
The first requirement of the design is a
method of sounding the horn, flashing the
vehicle's lights and breaklights simultaneously when the alarm is activated. Whilst
maintaining complete isolation between
these circuits while the car is in normal use.
The second design requirement is a method
of driving a continuous supply of 12 volts
for a siren from the pulsating DC alarm
signal without recourse to a large capacitor
and the resulting slow run down of the siren
when the alarm is switched off.
The project outlined has combined
these two requirements into a compact
weather resistant housing suitable for
mounting in the engine compartment.
Compu-Tech's add-on alarm control module comes complete with
weather resistant housing to give trouble -free service from its hiding
place.
Add-on Power
The current rating of the Alarm Control Module is 15 A, which is adequate for
the demands of vehicle horn circuits ranging from seven to twelve amps. In order to
meet the increased current demands of the
vehicle lighting circuits, which range from
six to ten amps, an additional fused circuit,
independent of the Main Alarm Control
Module, must be provided and independently switched by the alarm signal.
Construction
Construction is straight -forward with
the Compu-Tech kit Of course, this little
project must be used in conjunction with
the ETI Car Alarm (Dec. 1978). Photocopies
of this article are available from ETI for 50
pence.
50
Undo the snap -on front of the plastic housing and there's the compact
PCB nestling inside.
ETI APRIL 1980
PROJECT
R1
47R
FUSED +12V
15A SUPPLY 8
C1
4u7
ZD1
15
VOLT
16V
ZENER
FROM TERMINAL
NO.15 OF MAIN
7
Q
CONTROL MODULE
EARTH
s
0)
D1
6
D
D7
0
+
/ /I
HORN
5
IC1a
RLA1
C2
2
/T
1N5401
0
4u7
16V
14
8
D
BRAKE LIGHTS 4
o
D4
IC1d
10
9
1N5401
R2
D5
HEADLIGHTS
SIREN+
3
t7
2
0
470k
I
12
1N5401
\
11
13
06
R3
2k2
Q1
SIREN --
02
1
TIP31A
R4
W^
BC337
180R
-AA/VR5
180R
NOTES
ALL DIODES ARE 1N4148 UNLESS OTHERWISE INDICATED
IC1 IS CD4001AE
:
'-/\A/v\-Fig.1. Circuit diagram. For ease of identification the terminal numbers are marked
on the case front.
HOW IT WORKS
1 Hertz pulsating alarm signal from the
Main Alarm Control Module is connected to
the Flasher Module via terminal (7). The
horn output is derived directly from this
signal at terminal (5) via blocking diodes D2
and 03. The signal from the alarm control
module also energises RLA1- D1 absorbs
the spikes created by the collapsing magnetic field of RLA1 which occurs during the
pause in the alarm signal. Whenever RLA1
energises the second DC supply provided at
terminal (8) is switched to the brakelight
circuit at terminal (4) via blocking diode
D4 and to the headlight circuit at terminal
(3) via blocking diodes 05 and D6. Blocking
diodes D2-6 ensure that the horn, headlight
and brakelight circuits remain isolated when
in normal use.
The
The
supplies
and also
via Rl.
DC supply provided at
terminal (8)
the siren directly via terminal (2)
supplies the internal logic circuitry
ZD1 limits the DC supply to 15
volts which protects the IC from spikes that
may be present on the incoming supply. Cl
filters out any noise that may interfere with
the operation of IC1. IC1 is connected as a
set -reset flip-flop. This arrangement provides
a quick snap action to switch the siren on
ETI APRIL 1980
and off thereby avoiding prolonged rundown of the siren. The alarm signal, when
present at terminal (7), is coupled to IC1 via
D7. The alarm signal will charge C2 to 12
volts which is sensed as a logic '1' by IC1
locking it to a stable state with a logic '1' at
the output of IC1b/IC1c. IC1b is parallel
with ICic for increased output current drive
capability. The logic '1' present at the output of IC1b/IC1c drives a modified darling ton pair consisting of R3, Q1, R4, R5 and
Q2 into conduction which provides an earth
return path for the siren at terminal (1).
This particular darlington configuration
exhibits a very low saturation voltage across
Q2 when it is conducting which minimises
the power losses that would occur with a
conventional darlington saturated switch.
D8 absorbs the spikes created by the commutator in the siren. The time constant of
C2 and R2 is approximately two seconds
which is twice the period of the alarm signal
from the control module. Therefore, the
pulsating alarm signal will be seen as a
continuous logic '1' as long as the alarm
signal continues. Once the alarm signal is
reset C2 will discharge to a logic '0' which
will reset the set -reset flip-flop to its quiescent state with a logic '0' at the output
of IC1b/IC1c silencing the siren.
BUYLINES
Corn pu -Tech Systems, Laundry Loke Industrial Estate, North Waisham, Norfolk will
supply a complete kit of parts for this
project including wire, connectors and
hardware for £11.95; Siren £7.75 extra.
(PCB only: £1.00).
A prerequisite for proper operation of
this project is the installation of the Vehicle
Alarm Project in the December 1978 issue
of ETI. A complete kit of parts for this
project which also includes wire, connectors, hardware and switches is still available
for £14.75. (PCB's only: £1.00 each).
Both projects and Siren for £29.95.
(Prices are all inclusive; UK only).
51
PROJECT:
Car Alarm
NOTE FLAT SIDE
..LaLat::21
NOTE METAL
Fig. 2. Component overlay.
Make sure you connect all
the diodes
round.
the
right
way
(2)
(1)
(3)
(4)
(5)
(6)
(7)
(8)
PARTS LIST
RESISTORS
SEMICONDUCTORS
1C1
CD4001AE
Q1
BC337
TIP31A
42
01,7,8 1N4148
47R
470k
2k2
R3
R4,5
180R
CAPACITORS
C1,2
4ù7 16V tantalum
R1
R2
D2-6
ZD1
1N5401
15V 400 mW zener
MISCELLANEOUS
12V relay, 120R with s.p. nie contacts.
Compu-Tech Systems' kit of components for this project includes a smart,
compact snap -front, weather resistant
case. When using an alternative, make
sure it's weather-proof.
HORN/HEADLIGHT/BRAKELIGHT/FLASHER
AND
SIREN DRIVER MODULE
O O O O O
FITTED INSIDE DASHBOARD OR
INSIDE THE ENGINE COMPARTMENT
el
el
el el
el
I.,
FITTED IN ENGINE COMPARTMENT
NEAR ONE OF THE HEADLIGHTS
C)
Fig.3. This is how you connect the box of
tricks to your wheels. You shouldn't
encounter any problems here.
O`^
1
jr."
<
GREEN
/7777
VEHICLE
EARTH
PINK
HEAVY RED
HEAVY VELLO
n
o
TO SOURCE OF FUSED
AND UNSWITCHED +12V
(CIRCUIT RATING IS 15A)
SO TERMINAL NO. 15 OF
MAIN CONTROL MODULE
HEADLIGHT CIRCUIT
(DIPPED)
RED
BRAKELIGHT CIRCUIT
HORN CIRCUIT
O
NOTE
THIS WIRE WAS PREVIOUSLY
CONNECTED TO TERMINAL NO.15
OF THE MAIN CONTROL MODULE
HEAVY
ORANGE
ETI
52
ETI APRIL 1980
FEATURE
ETI
CIRCUIT
COOK BOOK
Project Editor Ray Marston digs into his treasure chest of
'Tried and Tested' circuits and pulls out over fifty of the best
for his special ETI feature.
Power Amp Circuits
Awide range of special-purpose single and dual
ICs are available for use as audio power amplifiers giving
maximum
outputs from a few hundred milliwatts to a respectable
'several watts'. The specific IC chosen for a given
application depends
mainly on the constraints of the available power supply
voltage and,
on the required output power level or levels.
In cases where supply voltages are restricted
to the 6 to 12 volt
range and power levels less than a few watts
are needed, the
National Semiconductor LM388 range of ICs can be
used.
The LM388 uses a high -impedance gain -programmable
ground -referenced differential input stage that is
automatically
biased to a quiescent half-supply value, for maximum
non -clipped
output swing. In the interest of power efficiency, the output
stage
has no short-circuit protection network.
The output stage of the LM388 is designed for use with
a
bootstrapped external bias network. The LM390 is a similar IC
but
has an improved output stage which enables 1
watt to be fed to a
4R0 speaker load from a 6 volt supply. The LM386 is also similar to
the LM388, but has a simplified output stage incorporating
a builtin bias network. Finally, the LM389 circuit is identical
to the LM386
but additionally an array of three fully accessible NPN transistors
are built into the IC package.
Cl
10u
RV1
10k
VOLUME
VSUPPLY= 6V
VSUPPL V - 12V,
SPKR-4R0,
SPKR = 8R0,
POUTPOUT
Fig.1.3. Maximum available output power can
be increased by bridge
connection of a pair of LM388s, so that the power
losses are shared
between the two. RV1 is used to set the quiescent
speaker current to
zero.
MASTER
REMOTE
SPKR
ORO
Fig.1.1. The outline and equivalent circuit of the
LM388 1.5 watt
device, specifically designed for low voltage
applications. The IC has
a built-in 'frame', which acts as a heatsink
and is connected to six of
the IC pins. Power dissipation can be enhanced by soldering
to a large area of copper track on a PCB, which thus serves these pins
as an addi-
1W
= 3.5W
SPKR
8R0
Fig.1.4. An LM388 can be used as a simple intercom
circuit. The IC
voltage gain is set at 300 by the C3-R3 decoupling network.
BYPASS
-
14
- V+
+INPUT
NC
tional heatsink.
GND
GND
-
INPUT
GND
-
8
7
NC
VO UT
LM 380
LM 384
IN
RV1
10k
VOLUME
SPKR
4R0 @ 6V
8
BYPIASS
OR 16R @ 12V
Fig.1.2. One way of using the LM388 as a 1 -watt non
-inverting
amplifier with grounded speaker. The voltage gain is internally power
set at
20. R1-R2 are the output stage bias resistors,
bootstrapped by C4. C3
improves supply ripple rejection and C2 provides
high frequency
decoupling. The dotted C6-R3 components (also
shown in all other
practical circuits in this section) form a Zobel network
that is intended
to damp parasitic oscillations from low -impedance loads
and should
ONLY be used if instability problems are experienced.
Fig.1.5. In cases where supply voltages are not restricted to
the 6 to 12
volts range and output powers of only a few watts are required,
the
popular LM380 2 -watt or its identical, but uprated LM384
5 -watt
'brother' can be used. These ICs have full output short-circuit protection and use the same type of heatsink 'frame' as the LM388.
2
ETI COOKBOOK
NEWS
DIGEST
Nevada News
rom January 5th to 8th a large
I- contingent of electronic retailers, wholesalers, agents and distributors once again descended
upon Las Vegas, Nevada for the
Winter
Consumer Electronic
Show - to date the World's largest
showpiece reflecting current and
future trends in audio, video,
computer games, telephones,
personal communications/computers and allied electronic products. This menagerie was staged
at three venues: the Las Vegas
Convention Centre, the Hilton
Hotel and the Jockey Club.
The emphasis from the Japanese contingets was centred on
remote control, including ultra
sonic, infra red, and voice control! That's right, I said voice control. 1980 could be the year in
which voice activated electronic
products finally live up to their
vast potential.
Industrial uses for voice activation are already in effect while
consumer products have yet to hit
the market. For example, in America United Parcels Service has a
voice activated parcel sorting system. Other industrial uses involve
warehousing and distribution inventory and quality control as
well as aids to the handicapped
such as voice activated wheelchairs.
One company, Heuristics Inc.
of Sunnyvale, California, has sold
between five and ten thousand
speech recognition units for use
with personal computers. However, all existing equipment requires close talking or a hand held
microphone, making it only
slightly more advanced than
many remote control units.
A television set that can be
operated by human voice and
confirms command is one of the
latest developments announced
by Toshiba. They also have a hi-fi
system which responds to fifteen
words. At a recent Japanese electronic show, Sharp showed a device able to recognise three voices, twenty-two words each. Such
products are speaker trained,
meaning each system can recognise onlyone or two voices. This
form of recognition will be prevalent for some time since speaker
independent systems, capable of
responding to a pre -trained vocabulary spoken by anyone, pose
extreme difficult technical and
pricing problems. An existing
ETI APRIL 1980
speaker independent system with
thirty words vocabulary sells for
$50,000. So, it seems in the very
near future, your hi-fi system will
truly respond to 'HIS MASTER'S
VOICE'.
Last year's magic phrase in video cassette recording waslonger
playing time. This year's magic
phrase appears to be special effects as supplies of both VHS and
Beta systems used this Winter's
C.E.S. to unveil a new generation
of feature laden home decks and
portables with such special effects
as visual slow motion, freeze
frame, single frame advance and
fast forward at up to fifteen times
normal speed.
Now the VHS camp has also
jumped into the visual scan
frame. Although JVC was the first
VHS supplier with visual scan
model, RCA, Quasar, Magnavox
and MGA have unveiled new
models with special effects visual
scan features. RCA coupled its
mid -December video disc announcement with the introduction of new 2, 4 and 6 hour decks
with visual freeze frame, variable
slow motion, single frame advance and double speed playback. All functions can be operated by remote unit and the suggested list price for the new deck
is $1,395. Hitachi also introduced
their model VT5800A. This is a
new 2, 4 or 6 hour deck with ten
key programming for up to seven
days plus a new lightweight camera which will sell in the US for
less than $800. Whilst the VHS
and Beta camps slug it out on the
video cassette recorder market,
Toshiba has added a dramatic
new element to the fight, marketing plans for the first consumer
LVR systems. Toshiba is introducing two units, the L1 0A (stan-
Hot 'n' Fast
his powerful little package can
deliver up to 75 watts in only
five seconds at the touch of its
fingertip control lever. The miniature iron uses the unique Scope
I
tion of the disc gives you one video frame.
So it appears on the surface
that the consumer is faced with
another non-standard consumer
orientated video product.
As television, audio and
games manufacturers add more
microprocessor controlled units
to their product lines, it seems manufacturers can count on expecting continued chip shortages
throughout 1980. When allocating chips, the semiconductor industries look more favourably on
such financially established industries as computers, television
and audio, according to sources
within the consumer electronics
industry. There has been a
demand for chips building up in
the television industry for some
time.
dard) and the Li OS with electronic programmable tuner and full
mode remote control. If Toshiba
realises its plans, the units will be
the first and only LVR's in the domestic market. BASF has shown a
competitive prototype in Germany, but has taken no further initiative so far.
Matsushita has the Visc system - Visc 2. It's the closest design
to normal a record with the information in the grooves of the disc.
All the above systems are totally
incompatible. 1,800 rpm is common to most of the systems. This
number is derived from the fact
that there are sixty seconds in a
minute and thirty seconds per
frame in US video, so one revolu-
carbon heater and is powered
from the Scope 3V3 transformer.
The Mini -Super -Speed Iron
costs £12.50 plus VAT, the 3V3
Safety Transformer £7.50 plus
VAT, and the element/tip spares
Metal Locator (March)
The Metal Locator project from
the March issue has already
caused quite a stir at Altek Instruments' office in darkest Surrey.
Now, do you want the good news
or the good news. Well, the good
news is that Altek have been inundated with orders to such an
extent that they have been able to
reduce their prices. The complete
kit is now £79.70. The search
head alone is £13.55. And now
It appears that both the audio
and video categories will get the
chips that they want for 1980.
Supplies of microprocessor audio
components which sell far fewer
units than the $500,000,000 electronic games industry report no
difficulties in obtaining chips. Almost every product in the future
will incorporate microprocessors
hence companies like Atari, who
have planned on introducing
eight new products, have to limit
themselves because of the shortage of chips.
There just are not enough
chips to go around. The games
industry has had a very steep
growth. In the last two years, a ten
fold increase in demand which is
still growing at the same rate, but
if the current trend in games diminishes, semiconductor manufacturers will be in embarrassing positions should they increase their
chip manufacturing facilities.
Gerald Chevin
pack £2.50 plus VAT. All Scope
products, which are manufactured in Australia, are available exclusively in the UK through Tool range Ltd, Upton Road, Reading
RG3 2JA.
the good news. Both prices include VAT and postage - no extras
to pay.
The Shadow VLF Metal Locator is available in kit form from
Altek Instruments, 1 Green Lane,
Walton-on -Thames, Surrey KT12
5HD.
9
FEATURE: Circuits
MAX
V+
LM377
LM378
LM379
OUTPUT POWER
CHANNEL INTO:
PER
8R0
12V
'
0;i
16V
1
'
JwZ
uf
n
oF=
18V
C5
20V
i
%Z
a
I-
ó
FO
22V
SPKR
8R0
,
ñL.Z
x
O Q
E
1W
2.2W
1.5W
3W
1.8W
3.8W
2.4W
4.6W
2.8W
ci
24V
26V
30W
16R
1.6W
5.4W
3.6W
6W
4.ZW
o
/I/A
7W
5.5W5W
SPKR
8R0
Fig.1.9. The approximate performance characteristics of the three
ICs. All three ICs have similar internal circuits with ground -referenced
differential input stages and fully protected output stages.
NOTE; LM379 PIN NUMBERS
SHOWN IN PARENTHESES
Fig.1.6. A simple inverting stereo amplifier using the LM377, LM378
or LM379 dual amplifier IC.
SPKR
URO
Cl
100n
SPUR
8RO
IC1=LM380, POUT=2W
V+=18V,
V+=22V, IC7=LM384, POUT=5W
VIN
C5
+
4700
RV1
47k
VOLUME
NOTE; LM379 PIN NUMBERS
SHOWN IN PARENTHESES
3
,
100,11.11
,12
Fig.1.10. A non -inverting stereo amplifier using
SPKR
8R0
+C3
a
split supply.
100
¡NS
13V
Fig.1.7. A 2 watt or
ripple rejection.
watt amplifier with simple volume control and
5
C4
NOTES
01 = TIP 41A
470n
02=TIP 42A
O
NC
Cl
100n
LEFT
II
CHANNEL0
6
IN
(9)
RS
14
4R7
LM3 8
100k
v
1
BIAS
OUTPUT
1
O
0 -1
AD
-0-
0--
o
NPUT 2
^L
1
FEEDBACK 2
FEEDBACK
1
1
0J
Oy-
R2
GND
OUTPUT
R3
2k2
100k
2
'C2
INPUT2
407
C5
R4
470n
C3
82P1
--r0
'
FEEDBACK2
8
LM377 DUAL
LM378 DUAL
4130
SIGNAL GND
O POWER
POWER UND O
INPUT
LEFT
SPKR
14 O BIAS
11/
I
PINS
(8)
O NC
NC O
OUTPUT
7
10,11,12
SIGNAL GNDO
GND
O
O
FEEDBACK
OUTPUT
O
O
INPUT
V+
D V+
O
GND
0
14
-0
0-
181
o
NOTE
-WATT AMPLIFIER
4 -WATT AMPLIFIER
:
PIN CONNECTIONS FOR IDENTICAL RIGHT
CHANNEL SHOWN IN PARENTHESES
2
-13V
/7777
OV
LM379 DUAL 6 -WATT AMPLIFIER
Fig.1.8. The outlines and pin notations of the LM377, LM378 and
LM379.
ETI COOKBOOK
Fig.1.11. One channel of a 12 watts per channel stereo amplifier using
split supply. The circuit produces negligible output DC offset, so the
quiescent output current is near zero.
a
Audio Preamp Circuits
Audio preamplifier ICs are specifically designed to give very
low noise figures, excellent supply 'ripple' rejection, low distortion and wide bandwidth. They give small -signal performances
that are superior to those obtainable with conventional op -amps.
IC pre -amps usually come in the 'dual' form, with two identical
but independent (apart from the supply connections) circuits in one
package. National Semiconductors produce a range of five popular
low-noise dual pre-amplifier ICs, the LM381 and LM381A, the
LM382, the LM387 and the LM387A. The 'A' suffix devices are
premium versions of their type, with superior low -noise figures.
All five ICs use the same basic amplifier circuit and essentially
differ only in minor details and in their pin -outs. All amplifiers
accept differential or single ended inputs, use internal compensation, use internal power supply decoupler - regulator circuitry and
can provide large output voltage swings and wide power bandwidths. The LM381 and LM381A have provisions for externally
optimising noise figures and for adding external compensation for
narrow -band applications. The LM382 has a built-in resistor matrix
that enables the user to select a variety of closed loop gain options
and frequency response characteristics. The LM387 and LM387A
are 8 -pin 'utility' versions of the LM381/LM381A.
In most of the practical circuits that follow, only one amplifier
of the IC is shown in use. Equivalent IC pin numbers forthe remaining amplifier are shown in parantheses.
The LM382, with its built-in resistor matrix, enables many
amplifier designs to be achieved with a minimal number of external
components.
The small physical size of the 8-pin LM387 and LM387A IC
makes it attractive for use in many low -noise pre -amplifier
RV1
2k7
BIAS ADJUST
Fig.2.3. A low -noise X1000 amplifier circuit. Bias is determined by
R3-RV1 and gain by R3-R4. R1-R2 set the amplifier to optimum
minimum noise conditions.
MAGNETIC
PICKUP
IN
applications.
RV1
-IN (DIFF)
-IN (SE)
(1)
-IN (DIFF)
C
-IN
(11 C
GND
(2)
+IN (1)
-IN
(SE) (2)
EXT COMP
1
C
1
OUT(1)C7
8I
Cj1
C
GND
C
V+
GAIN CONTROL (1)
C
OUT (2)
GAIN CONTROL (1)
OUT (1)
C
LM 381
OR
+IN (2)
3
11) C
GAIN CONTROL (1)
(2)
EXTCOMP rC
11)
2k7
BIAS
ADJUST
+IN (2)
+IN (1)
-IN
(2)
GAIN CONTROL
V+
D
C 7
8
D
(21
GAIN CONTROL (2)
GAIN CONTROL (2)
OUT (2)
LM 382
LM 381A
+IN (2)
+IN (1) '
-IN
(1)
.IN (2)
'
GND
OUT
Fig.2.4. The circuit shown in Fig.2.3 can be modified for use as an ultra
low -noise phono preamp, with RIAA equalisation given by the R5R6-C6-C7 network. The circuit gives 42 dB gain at 1 kHz.
V+
OUT(2)
1
LM 387
OR
LM 387A
Fig.2.1. Outlines and pin notations of the LM381, LM381A, LM382,
LM387 and LM387A.
LM381
VSUPPLv
9V
-40V
LM381A
9V
-40V
LM382
9V
-40V
LM387
9V
-30V
LM387A
9V
-40V
IOUIESCENT (TYP)
10 mA
10
mA
10 mA
10 mA
10 mA
POWER BANDWIDTH
75 kHz
75 kHz
75 kHz
75 kHz
75 kHz
(20V
pk-pk)
SUPPLYREJECTION
RATIO AT 1 kHz
(TYP)
NOISE
T
120 dB
120 dB
110 dB
TYP
9.5
0.5
0.8
0.8
0.85
1.0
0.7
1.2
1.2
0.9
)
4
low -noise tape playback
+9 T0 +40V
Cl
+9 TO +40V
OUT
40 dB AMPLIFIER
Fig.2.2. Typical performance of the five low -noise dual preamplifier
ICs.
as a
110 dB
884sMAX
NOISE INPUT
FIGURE
V
-120 dB
Fig.2.5. A simplified version can be used
amplifier, with NAB equalisation.
5545 AMPLIFIER
OUT
80 dB AMPLIFIER
Fig.2.6. Alternative methods of connecting the LM382 to make fixed
gain non -inverting amplifiers.
ETI COOKBOOK
FEATURE: Circuits
Fig.2.11. 50 Hz rumble filter with 12 dB/octave roll -off.
Fig.2.7. Fixed gain (X1000) non -inverting preamplifier. The gain is
determined by the ratio of R2 and R3. Alternative values of gain can
be obtained by changing the value of R2. The circuit is biased by
R1-R3.
LM387
IN
OR
LM387A
Fig.2.12. 10 kHz scratch filter with 12 dB/octave roll -off.
Fig.2.8. 12 V NAB tape playback preamp.
CHANNEL1
OUTPUT
1u0
LM387
OR
LM387A
CHANNEL 2
OUTPUT
Fig.2.13. This two channel panning circuit enables a mono input to be
swept or 'panned' between two channels in any desired ratio determined by RV1. It can be used to make a sound source appear to
originate from any point between two widely spaced speakers.
Fig.2.9. Low -noise microphone preamp with a gain of 52 dB. The
is intended for use with low to medium impedance microphones.
circuit
MAGNETIC
PICKUP
IN
Fig.2.14. RIAA equalised, single supply rail, pre -amplifier for magnetic pickup cartridges. Input impedance 47k, determined by Rl.
Fig.2.10. A high performance active tone control.
ETI COOKBOOK
5
i
Relay -Switching Circuits
Relay-switching circuits are popular and useful projects and
are always in demand by ETI readers. The relay may, depending on the individual circuit configuration, be made to switch
on in response to increases or decreases in light or temperature
levels, or by voltages or by currents going above or below pre-set
values. Alternatively, the relay may be made to turn on or off in
response to some time -delay factor, or may merely be made to
respond to the presence or absence of a voltage, as in the case of
some car anti-theft and immobilisation circuits. A wide variety of
such circuits are shown in the following section.
These are circuits that activate if a parameter falls outside of two
pre-set limits.
Figs. 3.10 to 3.12 show time -delay switching circuits. Figs. 3.10 and
3.11 operate in the simple 'C -R timing' mode and call for no
explanation.
To complete this section, Fig. 3.13 to 3.15 show a selection of car
immobiliser and anti -theft alarm circuits. The Fig. 3.13 circuit turns
on and immobilises the ignition automatically when the ignition
switch is first closed: the ignition can be re -enabled by briefly
Fig.3.3. A precision light-sensitive switch that activates when the
sensed quantities go above or below pre-set values. The LDR can be any
cadmium -sulphide unit that has a resistance in the range 500R to 20k at
the required trip level.
opening PB1.
The Figs. 3.14 and 3.15 anti -theft alarm/immobiliser circuits
are designed for use in cars with negative ground electrical systems.
Before trying to fit either of these systems, however, check that your
vehicle is fitted with door switches that connect the dome (courtesy)
light to chassis, as shown, when they are activated.
Fig.3.4. A differential temperature switch circuit using ordinary silicon
diodes as temperature -sensing elements and responding to differentials
of a fraction of a degree. RV1 can be used to apply an effective offset
of several degrees to the two diodes. To adjust the circuit, apply the
required differential temperature to the diodes and then adjust RV1 so
that the relay just turns on. The circuit responds to the relative temperatures, rather than the absolute temperatures, of the two diodes.
LOAD
Fig.3.1. A precision DC under -voltage relay switch. The op -amp is
wired as a voltage comparator, with a reference voltage applied to pin
2 and the test voltage applied to pin 3: the relay turns on when the pin
3 voltage exceeds that of pin 2. The circuit can be made to trip at any
voltage in excess of 5 volts by suitable choice of Rx value.
Fig.3.5. A DC current -sensing switch, in which the current is applied
from an 8 to 16 volt supply. The Rx value is chosen so that it generates
roughly 100 mV at the required trip current.
CLUSTER OF UP TO
4 SIMILARLY RATED
LAMPS ON A COMMON
HARNESS SECTION
OPTIONAL
RANGE
RESISTOR
ILOAD
_-
2V VIA LIGHTING SWITCH
SNAP
CONNECTOR
100mV
SNAP
CONNECTOR
RLA
12V
>120R
Fig.3.2. An over-voltage switch that can be used to trip at any pre-set
voltage in excess of about 10 mV. The input voltage can be connected
directly to pin 2 if trip values in the range 10 mV to 3 volts are required. For voltages in excess of 3 volts, a suitable range resistor must
be connected in the position shown, to keep the pin 2 voltage drive to
a suitable level. The circuit can be converted to an under-voltage
switch
by transposing the pin 2 and pin 3 connections of the op -amp. The
circuit can be used as an AC voltage switch by first rectifying the AC
input signal.
Fig.3.6. shows how the above circuit can be made to act as a car lamp failure switch which turns on if any of the monitored lamps burn out.
Rx is wired in series with the wiring harness feed to a selected 'cluster'
of up to four similarly rated lamps.
6
ETI COOKBOOK
FEATURE: Circuits
OPTIONAL
RANGE
RESISTOR
6-60
Fig.3.11. A two range
relay timer circuit.
Fig.3.7. A voltage -window switch. In practice the basic lower window
limit of this circuit is roughly 3 volts and the upper limit is 9 volts.
The window range can be extended by fitting a suitable range resistor
in the position shown.
1-10 minuted auto -turn-off
second and
IGNITION
SWITCH
Fig.3.12. An automatic immobiliser circuit for cars fitted with negative
ground electrical systems.
RLA
TO HORN BUTTON
SW1
DOME
Fig.3.8. is basically a resistance -sensing window switch, except that the
'resistor' takes the form of an ntc thermistor and the circuit thus
responds to temperature. TH1 must have a resistance in the range 500R
of 9k0 at the desired 'mean' temperature. RV1 is used to set halfsupply volts on the RV1-TH1 junction at the 'mean' temperature.
EXTERNAL
RLA
KEY SWITCH
12V
120R
(COURTESY)
LIGHT
131
1N4001
RLA
12V
TO HEADLIGHT SWITCH
3
1N4001
RLA
e
RLA
1
4
DOOR
SWITCHES
-
TOCBPOINTS
AUXILIARY
SWITCHES
Fig.3.13. An anti -theft alarm/immobiliser for cars, which operates horn
and lights until switched off or until the battery runs flat.
SW,
EXTERNAL
KEY SWITCH
D4
54001
DOME
(COURTESY(
LIGHT
01
1N4001
OS
1N4001
Fig.3.9. A sensitive switching circuit that responds to AC inputs in
excess of about 5 mV rms. It responds to all signals in the 50 Hz to
3 kHz 'voice' range. RV1 is adjusted so that the relay is just off with
zero input.
r
RLA TO CB POINTS
2
b
RLB
Fig.3.10. A 100 second delayed -turn -on relay switch.
ETI COOKBOOK
RLB
+
2
f
a +
TO HORN BUTTON
TO HEADLIGHT SWITCH
Fig.3.14. An improved car alarm/immobiliser, which disables the
ignition indefinitely but turns the horn and lights off automatically
after four minutes.
7
r--
GANGED
D1
R5
1N4001
12k
k2
C3
100n
BC214L
RLA
R6
16
6k8
2
10
o
CD40178
R2
START
Q1
9k
CD4020B
11
555
TIMER
3
RV1
470k
TIME
D2
ßwla
R3
1M0
2
Cl
T2an
RLA
12V
>120R
R4
27k
104001
-
RANGE 1 = 1
12 MINS
RANGE 2= 10MINS -2 ORS
RANGE 3 - 100MINS
20 ORS
-
C2
Pul
POLYESTER
OV
o
Fig.3.15. A wide-range auto -turn-off timer covering 1 minute to 20
hours in three ranges. As soon as power is applied to the circuit the 555
starts to oscillate happily and feeds clock pulses to the 4017. The 4017
and 4020 give a combined count rate of 81920 before the output of
the 4020 goes high and turns Q1 on.
Fig.3.16. Precision DC over -voltage relay switch, covering 5V up-
wards.
PB1
START
-j
Fig.3.18. A sensitive (1 kHz) tone activated relay switch, which
typical sensitivity of 5 mV RMS at the input.
has a
O
+12V
0V
8
Fig.3.17. Precision over -temperature, or 'FIRE' switch. This circuit
'frost' or under-temperature switch by transposing RV1 and TH1.
can be converted to a
Fig.3.19. A delayed turn-off relay switch. With component values of
R1 and Cl as shown, the time delay is determined at 100 seconds.
ETI COOKBOOK
FEATURE: Circuits
P81
START
+12V
D1
154001
12k
2k2
C3
100n
BC214L
I
RL
__A
R5
7
39k
2
6k8
10
555
TIMER
CD4020B
RV1
470k
TIME
SW1
03
IMO
10-100
MIN
RLA
12V
>120R
D2
1N4001
I
1-10 MIN
DDn
1u0
POLYESTER
OV
o
Fig.3.20. A two -range 1-10 minute and 10-100 minute auto turnoff relay timer circuit. Different ranges can be obtained by varying
the values of capacitors Cl and C2.
D1
1N4001
12k
2k2
01
BC214L
C2
100n
7
R5
PB1
START
+12V
RLA
1
8k8
R2
3
39k
2
14
CD4020B
CD4017B
555
TIMER
RV1
470k
TIME
R3
1M0
RLA
1
D2
154001
V
>120R
1u2
POLYESTER
OV
o
Fig.3.21. An extra-long period timer, which could be used as a long
process cycle controller. The period obtainable from this circuit is
between 100 minutes and 20 hours. Auto turn-off operation has
been selected.
Waveform Generators
Waveform generatorcircuits are widely used both as pieces of
test gear and as simple 'noise making' gadgets. Types of
waveform generated range from accurate sine, square and
pulse waveforms to 'mushy' white and pink noise forms.
If you need a variable sine wave generator for audio or ultrasonic testing purposes, you are faced with a number of circuit
choices, depending on which parameter you consider to be most
important. If low cost is important and a distortion factor of up to
0.5% is acceptable, the lamp -regulated Wien -bridge oscillator (Fig.
4.1)
good choice.
If low distortion
is a
is your most important parameter, the thermistor-regulated Wien -bridge oscillator in Fig. 4.2 is a good choice.
This circuit typically produces about .05% distortion at kHz and
shows how range switching can be incorporated.
If minimal bounce is your most important parameter and a
distortion factor of 0.5% is acceptable, the circuit of Fig. 4.8 is an
ideal choice. The circuit uses a special function generator IC (available from several ETI advertisers) and a single frequency-control pot
and spans its frequency range with absolutely zero bounce.
1
ETI COOKBOOK
If you ever need to generate a fixed or variable HF or RF signal
you'll have the option of using either a Hartley (Fig. 4.4) or a Colpitts
(Fig. 4.5) oscillator. The Hartley oscillator uses a tapped coil and is
easily tuned over a wide range.
If you are a dedicated 'radio' listener you'll need a BFO circuit
to enable you to listen to CW transmissions. Fig. 4.6 shows a
practical BFO unit. An alternative BFO circuit is shown in Fig. 4.7.
Square wave forms are very easy to produce. The circuit in Fig.
4.8 can be used to generate a variable -frequency variable-mark/
space ratio waveform. Two excellent CMOS square wave generator
circuits are shown in Fig. 4.9. Both circuits produce clean output
waveforms and can accept a very wide range of C - R timing
components.
Pulse generator circuits can be readily built from standard 555
timer chips or from CMOS ICs, but in these cases have typical rise
and fall times of a hunderd nanoseconds or so. Where brief rise and
fall times are important (as in standard test gear circuits), TTL ICs
offer a good solution to the pulse -generator problem. The 74121 N
monostable multivibrator IC (in either standard or LS form), for
9
example, produces pulse rise and fall times of only
a
produces a +3 dB rise in amplitude per octave of frequency change
(equal energy per constant bandwidth). Pink noise has a flat amplitude response per octave change in frequency (equal energy per
octave). White noise is best produced by a pseudo-random sequence generator, such as the MM5837 shown in Fig. 4.12: unfortunately, this IC is rather difficult to find. The MM5837 is housed in an
8 -pin package.
White noise can be converted to pink via a simple filter network, as shown in Fig. 4.13.
few nano-
seconds.
Fig. 4.10 shows how a 74121 can be used as an add-on pulse
generator, triggered by an external clock signal. Fig. 4.11 shows
how two of these circuits can be cascaded to make an add-on
delayed pulse generator in which both the delay and the width can
be varied from 100 nS to 100 mS.
White and pink noise sources are widely used for testing
amplifiers and for generating special sound effects. White noise
9V
0-
1%
RV3
27k
(LEVEU
(SYMMETRY)
OV
GANGED
FINE
RV2
47k
OUTPUT
X0-2
J
OV
Cl= 1u0,f= 10HzC1=100n,f=100Hz-
RV4
470R
(SET 2V rmr.
(FREQUENCY\
RV5
1
206
Cl-
0
OUTPUT
o
100Hz
1kHz
10n,f= 1kHz - 10kHz
Cl= 1n0,f=10kHz-700kHz
(THD
R2
1k0
L
LP)
ANY 12-28V
LOW CURRENT
( <SARA) LAMP
+
RV3
10k
LEVEL
C3
10,
R1
10k
+
OUT
C4
RV1
100k
log
V
t0u
(FREQUENCY)
Fig.4.1. A low-cost 150 Hz
-
1k5 Hz lamp -regulated Wien -bridge
oscillator, producing a sine wave with a typical distortion factor of less
than 0.5%. The frequency range of the circuit can be changed by using
different C1-C2 values. Reducing the values by a factor of ten (to 10n)
raises the frequency range by a decade (to 1k5 Hz
15 kHz). The
specified op amp will give useful operation up to about 150 kHz. LP1
can be any 12
28 V low current (less than 50 mA) lamp and the
circuit is set up initially by simply adjusting RV2 to give a nominal
maximum sine wave output of about 2V5 RMS.
-
-
oV
Fig.4.3. The high quality function generator IC produces `bounceless'
sine waves with typical distortion factors of 0.5%. Initial setting up is a
matter of twiddling with the RV2-RV3-RV4 controls to obtain a
minimal distortion output signal with a maximum RMS value of about
2 V. Once you've initially set up the circuit, you can forget these pots
forever. The frequency range is controlled by RV1 and Cl.
Fig.4.4. In the Hartley oscillator the frequency = 1/27T
must be a tapped inductor.
V
JL1 C1
x L1
NOTES
SW1 RANGES
1= 15Hz -200Hz
2-150Hz -2kHz
3 =
1.5kHz - 20kHz
Fig.4.2. This low -distortion (0.05% typical) Wien -bridge oscillator
spans 15 Hz to 20 kHz in three decade ranges (with the component
values shown). The only defect of this low -distortion type of circuit
that it suffers from 'amplitude bounce' as the frequency is varied
from one value to another, which is a bit of a pain if you are testing
the frequency response of an amplifier. The degree of `bounce' depends
on the quality of the pot used in the RV1 position.
is
Fig.4.5. In this 37 kHz Colpitts oscillator the frequency = 1 /21r\/ L1 Cx ,
where Cx is the equivalent series capacitance of Cl and C2. L1 is
untapped. It is effectively an `autotransformer'tapped by the Cl -C2
ratio.
ETI COOKBOÓK
FEATURE: Circuits
BD®.
OUT
4011B
(b)
NOTE.
01
BC109
Fig.4.9. Two excellent CMOS square wave generators are the Schmitt
oscillator (a) and the ring -of -three oscillator (b). Both circuits produce
clean otuputs. `R' values can be varied from a few kilohms to many
megohms. 'C' values can vary from a few dozen picofarads to many
microfarads.
= ANY 465 KHZ TRANSISTOR
I.FTRANSFORMER.
TI
AF INPUT
(FOR A.M. OUTPUT)
Fig.4.6. A 465 kHz BFO with amplitude modulation facility. T1 can
be any standard IF transformer The output can be modulated via an
AF signal.
Cl
=
Cl
Cl
Cl
Cl
=
=
=
=
Cl=
RV1
22k
(WIDTH)
100p, WIDTH= 100uS
1n0, WIDTH= 1u5
10n, WIDTH =10,5
100n, WIDTH = 100,
1u0, WIDTH = 1mS
10u, WIDTH = 10mS
-
luS
-10,5
-100,5
- 1mS
- 10mS
- 100mS
OUT
CLOCK
INPUT
T1= ANY 465 KHZ TRANSISTOR
I.F. TRANSFORMER
RV1
10k
TUNE
Fig.4.10. An add-on pulse generator covering the range 100 nS to 100
mS, using a 74121 triggered by an external clock signal. The circuit
produces fixed amplitude inverted and non -inverted outputs, each protected against short-circuit damage by a 47 R series resistor. By suitable
choice of the value of Cl the triggered pulse width can be varied from
100 nS to 100 mS.
C4
1
OUT
a,
A F INPUT
(FOR F.M. OUTPUT)
Fig.4.7. A 465 kHz BFO with `varicap' tuning and FM facility. D1 is
used as a varicap diode and the oscillator is tuned via RV1. The oscillator can be frequency modulated via an AF source.
HV1'
-
22k
131
1N4148
f RANGE =110
M/S RANGE
T
= 11:11
-5
(DELAY)
1N4148
RV1
tOk
(MIS RATIO)
TO 1:111
PULSE OUT
9V
PULSE OUT
]
CLOCK
INPUT
LF356
02
100k
DELAY
OUTPUT
9V
RV3
10k
(LE.0
Cl
tOn
RV2
100k
(FREQUENCY)
C1/C3
OUT
100p
OV
100n
1u0
1n
10n
10k
o
Fig.4.8. A variable -frequency, variable M/S ratio 'square wave' generator. The mark/space ratio is controlled by RV1, the frequency by RV2
and the output level by RV3.
ETI COOKBOOK
10u
WIDTH
100nS
luS
10uS
100uS
1mS
10mS
- tuS
- 10uS
- 100uS
- 1mS
- 10mS
- 100mS
Fig.4.11. An add-on delayed pulse generator covering delay and width
ranges of 100 nS to 100 mS.
11
O
.5 TO 15V
R7
*lie
10k
4k7
4
WHITE NOISE
OUTPUT
R5
100k
R3
4k7
IC2
555
R2
47k
6
IC1
TIMER
L.4
C3
100u
555
TIMER
Fig.4.12. The National Semiconductor's MM5837 is an MOS/MSI
pseudo -random sequence generator, designed to produce a broad -band
white noise signal for audio applications. It is housed in an eight pin
package.
-r
1000
TOTAL
R6
2k7
BC214L
SPKR
ORO TO
100R
C2
10n
+C7
100.
00V
mn
Fig.4.16. This wailing alarm simulates an American police siren.
o
5TO15V+Ve
R1
10k
4
RZ
PINK NOISE
OUTPUT
01
1N4148
33k
R4
tC1
6
4k7
555
TIMER
IC2
555
TIMER
12k
2-1
100u
R5
2k7
1006
TOTAL
Fig.4.13. Pink noise generator.
SPKR
8130 TO
100R
+
il
7u
D1
0V
o
5TO15V+Ve
1N4001
TO PIN 14
/777
IC1
+
Fig.4.17. This 'Red Alert' generator simulates the 'Star Trek' alarm
C3
100u
signal.
SPKR
R3
8R0 TO
1000
NOTE
ICI IS CD4001B
100R
47k
TOTAL
1N4001
BC109
TO PIN?,
ICI
V3
10k
(LEVEL)
Fig.4.14. This pulsed -tone alarm call generator produces
put of a few hundred milliwatts.
a
OUT
typical out-
Fig.4.18. An op -amp relaxation oscillator producing
500 Hz to 5 kHz square wave.
a
good quality
5 TO 15V +Ve
10k
8
R5
220k
02
68k
6
IC1
555
6
102
C3
555
TIMER
10 u
TIMER
R3
10k
1006
TOTAL
+
Ti
10u
SPKR
TO
100R
ORO
C2
10n
0
0V
/7777
Fig.4.15. This warble-tone generator simulates
Dee-Dah'siren.
12
a
British police car
Fig.4.19. A variable-frequency, variable mark -space ratio square -wave
generator which takes longer to say than it does to build!
ETI COOKBOOK
NEWS: Digest
Text To Talk
sound with the speech synthesiser.
KurzwellComputer Products of
Massachussetts
has developed a machine to turn
written text into speech.
Syntax analysis is also incorporated to ensure that the right stress
is placed on the correct word in a
sentence.
The machine contains an optical scanner, a small computer, a
small synthesiser and a loudspeaker unit.
The optical system can accommodate a wide range of type
faces, but must be programmed to
do so.
The page to be read is placed
over the scanning unit which then
converts the written text to digital
signals for the computer. The
computer then converts them into
If the machine is a success it
offers enormous benefits to the
blind. It is curently being tested by
the Royal National Institute for the
Blind.
Cambridge,
Building Block
allowing it to function as a basic
building block in a broad range of
electronically programmable re-
New from National Semiconductor, the LM13600 is a programmable dual operation transconductance amplifier designed to be
sistors and filters. Use of novel cir-
cuit technique incorporating linearising (Gilbert) diodes on the inputs so they can accept higher
level signals while reducing distortion results in 10 dB S/N ratio
improvement reference to 0.5%
THD.
The recently announced Dolby
HX Headroom Extension System
for noise reduction uses the
LM13600 for dynamic control of
recording bias.
The remarkable LM13600 is
made by National Semiconductor
(UK) Ltd., 301 Harpur Centre,
Horne Lane, Bedford.
used as a fundamental building
block in current controlled amplifiers, filters and oscillators. It can
also be used in multiplexers,
timers and even sample and hold
circuits. In some cases it could be
used to replace mechanical po-
tentiometers. It is well suited for
use in electronic organs and
music synthesisers, because it can
modulate waveshapes with ease.
The 16 pin LM13600 is programmable over six decades,
ject, you might want to fit it with
handles, feet, knobs and/or
switches. West Hyde have them
all. Their latest catalogue has details of these and much, much
more.
The latest copy of this 80 page
Alladin's cave is available free of
charge from West Hyde Developmnets Ltd., Unit 9, Park Street Industrial Estate, Aylesbury, Bucks
HP20 ET.
Case Study
CB finished and nowhere to
put it? Well, we can tell you
where to go. You can get nearly
1000 different instrument cases in
almost 650 sizes from West Hyde
Developments. That includes a
new range of 19" housings and
keyboard, VDU and display
I
enclosures.
Once you've cased your pro-
Gps1á5ep5
(
PCB OFFERS
LB ELECTRONICS
-
(1A) 100 bit shift register PCB,
115mmx94mm
containing
9x7491, 6x7496 and 1x7441.
Terrific bargain 85p, p&p 30p.
(1B) Audio amp PCB (LM 380)
9-18v d.c., output 21/2 watts into 8
ohm with heatsink. 1.25 watt
4ohm without heatsink. £1.50
p&p 25p.
(1C) PCB 215mm X 290mm
12 xTMS 3122) or sim.)Hex
32 -bit Shift Reg. + (39 ICs. £2. +
50p p&p (limited stocks).
MPU CORNER
2112 (200ns) £3. 2114 (450ns)
£4.50.
1702 £2.50. 2708 (400ns)
£7.25.
2716 (Single Rail) £28.50.
74125 4 for £1 + p&p 257.
MK 1002P ( dual 128 bit Shift
MM5240 Character Generator +
Data 2560 Bit (64 x 8 x 5)
£3.50, p&p 25p.
-
CONNECTORS
D TYPE
15 Way: wirewrap, plugs only
757
25
25
37
50
50
Way: ribbon plugs £1.20.
Way: ribbon sockets £1.20.
Way:I
P9 £1.40, skt £1.40.
45,
Way:skt
a p)
£1.65.
Way: skt £1.45, p&p 257.
(
COVERS
37 Way: 80p.
DISPLAYS
MAN 72 7 seg CC £1.25, p&p
25P
Burroughs Panaplex 9 Dig. + skt
and bezel £1.00, p & p 25 p
LED 3 Digit
DIL 55 p, p&p 25p.
g
ETI APRIL 1980
PL259 (UHF) Elbow Connectors,
-
Bit, Dil packaged, ideal MPU users
with data, £2.95, & P 25 P
SUPERSAVER 5
LM 323K Voltage Regulator, 5 volt
3A, £4.50, p&p 25p.
SUPERSAVER 6
338-383 Miniature Decade
Thumbwheel Switch, £1.65, &
RS
50p each, p&p 25p.
SUPERSAVER 14
S423 Stud mounting rectifiers,
440v, 10A, giveaway price, 10 for
£2, p&p 25p.
SUPERSAVER 15
20K Painton multiturn trimpots,
PCB mounting, per box of 14
£2.50, p&p 25p.
SUPERSAVER 16
Astec UM 1163E 36 modulator
plus PAL colour PCB (faulty). Few
only £2.25, p&p 30p.
1
-
.
25
p
p'
p
SUPERSAVER 7
Dual 4 Bit letch 757,
p&p
p&p 25p.
SN7418 Arithmetic Logic Unit,
8074 p&p 257.
SN741944 Bit Shift Register, 507
p&p 25p.
SN741988 Bit Shift Register. 75p,
p&p 257
SUPERSAVER 8
BC tOBb 8p each or 100 for
£7.00, p&p 25
SUPERSAVER 9
4 Di g''t 7 se g meet LED Bubble
Display, NSA 154OÁ Ex equipment, 5 for £1, p&p 25p.
SUPERSAVER 10
9 way male/female connector,
ELCO 8129, 0.1 inch pitch, gold plated PCB mounting, ideal for
bussing two PCBs together.
Superb value, 35p, p&p 25p.
SUPERSAVER 71
STAR OFFER. Dynamic hand
microphone 200 ohm with lead
and 5 pin plug. £1.25 (unrepeatable) p&p 307.
SUPERSAVER 12
TMS 3128NC Static shift register,
9
£1.50, p&p 25p.
LEDs (Full spec).
TIL209, red, 10p. 0.2in, red f2p.
0.2in. green 28p. 0.2in, yellow
28p.
RL54 red Axial lead, 157.
P&P on all above 25 p.
VERNITRON Ceramic filters type
Yp
10 ?MHz 45p, p&p 25p.
P.
BC183L 10p, 8E195 10p, SGS
2N3055 30p, p&p on all 25p.
TBA 8105, with data, 85p, 4-way
Oil switches, 75 p, MC1303 Dual
Stereo preamp with data, £1.25.
7in. Nylon cable ties 100 for
£1.50. All p&p 25p.
NEW SN76477 (Yes, back in
stock). Sound Generator IC (Train,
plane, explosion, laser gun etc.),
with data £3.25, p&p 25p.
PCB
KEYBOARD,
65mm X82mm, 18 Key Clickers
less Key tops, ideal Hexadecimal
use 35p, p&p 25o.
PACKAGED 10 -WAY REED
relay 12V coil terrific value 507,
p&p 25p.
PAPST min -fans 80mm X 80mm
(approx) 2203 50Hz. Brand new
£8, p&p £1 (limited stocks).
NEW PERANCEA CLASES:
These superb cases now stocked in
the DIN range incorporating the
following features. Matt black fin-
snapfittinginto
front, firmly retaining
case
of the
front panes provided, one
one
RED
anti-
reflective. Each case has two sets of
guides with rear panel slots for PCB
mounting.
Types available.
1456
H48xW96xD75(mm)
DIN 2368
H36xW72xD120(mm)
P&P 25p. SAE for leaflet.
DIN
£3.75
£3.00
WE STOCK PETS
£599. SAE for PET
SORCERER software lists at discount prices.
We can also offer a 48 -hour repair
service for out of warranty PETs.
8K version
Telephone for details, PET edge
connector 40x04 £1.40 each p&p
25
25p.
40p
TRANSISTORS, BD236
fished bezels
NPPEQDSßPJs
aluminium,
SUPERSAVER 13
Reg)FM4
35p.
LM711CH (Voltage Comparator)
30p.
(All Full Spec)
SUPERSAVER
Ribbon Cable Headers 16 DIL
Jermyn, gold plated, with cover
4574 p&p 257.
SUPERSAVER 2
Tantalum Capacitors 25 volt, 4.7
uF, 14 for £1.00, p&p 25p.
SUPERSAVER 3
Mercury Batteries 1.35v 1AH. Db.
15mm, height 18mm, 35p, p&p
25p.
SUPERSAVER 4
HYBRID SYSTEMS DAC 371-8 8
1
IC HOLDERS
8 Dil 127
16 Dil 17
22 Oil 28p
28 Dil 45p
WE STOCK
'
(Low profile)
p
)
14 Dil. 15p
18 Dil 20 p
24 Dil 35p
All p&p 35p
vast range of TTL,
CMOS, some 74LS, MINIATURE
TOGGLES, etc.
PSUs. We have a large stock of
power supplies at very realistic
prices (callers).
a
RELAYS
ITT 700 ohm Single pole
changeover. 45p BANOR resettable double pole changeover 12V
£1, both p?p 25p.
.CIRCUIT BREAKERS
450v AC 65v DC 0.5A 50p; ditto
7A 80
& 25
ALLEN KEYS. p/ 16" 5p; 12 for
50p, p&p 20p.
Olivetti line printer with tape punch.
UXBRIDGE
55399
Full/Half duplex, 80 chair, per
Tine. £250 + VAT.
1 ONLY GEC 9000 Visual Display
Unit. Green phosphor, cursive
character gen. 600/1200 baud
asynchronous serial £95.
Shugart
801/8"
drive (fully)
tested on exercisor) £300 inc. of
VAT.
Terms cash with order (official
orders welcomed from colleges,
etc).ricAll enquiries
es
All
prices inclusive of VAT, unless
otherwise stated. Postage as
shown per item.
FOR THE PROFESSIONAL
USER. Gould mg5-208 PSU 5V
20A. Brand new and boxed
(switching) £65 p&p £3.
Gould PMA 47/10 0-15V 3A.
Brand new £45 p&p £3.50. Many
more instock but in smallor
numbers. Please phone for
requirements.
PLEASE DO NOT ORDER GOODS
FROMFOOLD ADVERTS. PHONE
BEFORE ORDERING.
LB ELECTRONICS
11
HERCIES ROAD
HILLINGDON, MIDDLESEX
U6109LS, ENGLAND
All enquiries s.a.e. please
New retail premises, now open
Mon:, Thur.. Fri., and Sat. 9.306.00. Lunch 1-2.15 weekdays.
We are situated just off the A40.
Opposite
Master Brewer,
pp
and reader, upper and lower case.
With stand £195. Phone for more
details.
Bu> u With .hxrs,
ONLY MOORE REED miniport
DT106 portable data terminal.
110 baud keyboard /printer with
7.11311W
internal modem and ACOUSTIC
t
COU PLeR tan
ASCII
to111===111)
telephone. Standard ASCII code.
1
UXBRIDGE
55399
All components full
spec.
l
11
FEATURE: Circuits
Test Meter Circuits
HIGH
R2
R3
R4
R5
390k
47k
220k
27k
R6
120k
R7
138
18
68k
R10
39k
R9
10k
R11
R13
R15
R16
R17
4k7
27k
15k
6k8
1k
R18
3k9
2k7
R23
1k5
R25
1k8
R20
27k
R22
18k
R24
150k
R21
R19
470R
INPUT
100k
LOW
00.85V
0.45V
02.5V
01.5V
R14
R12
270k
0
04.5V
8.5V
OV
180k
0
045V
025V
15V
0
85V
150V
250V
SW1
R28
15k
R30
C3
33k
+15V
R32 4 -11F--220k
8
12 7
11
C--4
15
150p
J
+15V
3
7
IC2
1494
3140
6
IC1
4
I-
+15V
7
14
301
IC3
o
+ -j4
RV3
R26
10k
1k
-15V
-15V
4
3
R27
10k
13
OV
833
6800
RV1
20k
R29
15k
--A,AAA
R31
100k
-15V
1mA
FSD
RV2
20k
OV
OV
Fig.5.1.. A true RMS voltmeter. The input voltage is divided by the
input network such that the input IC1 is 0.47 volts (DC or RMS) for
full scale deflection. IC1 provides buffering and a gain of two.
Squaring of the output of IC1 is done by IC2 (1494), a four
quadrant multiplier, which gives a current output proportional to
the produce of the voltages at its two inputs (pin 9 and 10). As we
are feeding the same signal into both inputs the result is the square
+15V
function.
The output of this IC is a current which is converted to a voltage
by IC3 which also provides the averaging network (C3, R32). Its
output drives the meter whose scale is a square root function.
Adjustments are provided for the input offset of 1C2 (RV1)
output offset (RV2) and overall calibration (RV3).
As the power requirement of all the ICs is ±15 V we use a mains
supply and three -terminal regulators. Current drain is about 15 mA
on both supplies.
OV
-15V
S2
OUT
R7
12V 20mA
PILOT
560k
6
R5
R2
R1
S3
10k
4700
C4
100n
7k
T
JBATT.
6
7
MAINS
C5
REF
R8
5
4
01
03
Cl
IC1
tk5
3n3
70k
2x9V
100k
I
010
+
1M
OUT
3
02
R11
10M
C21.
2
C6
640
25
D1
EM401
12.6V CT
150mA
R12
04
1M
120R
R6
T1
1k5
-R12 ARE 10W, 1% OR 2%
RESISTORS OR SELECTED
5% RESISTORS. ALL OTHER
RESISTORS `/.W, 10%.
Cl, C3 ARE POLYSTYRENE
OR SILVER MICA.
R7
i.
R9
8
TRIGGER
NOTES:
IC2
I
1
C3
1000p
R13
1k5
RV1
CAL.
110k
M1
0-1mA
EDGEWISE METER
OR OTHER
SUITABLE TYPE
1.pT
01--202646 e
6
IC1
NE555 IDILI
78L12
02
BC107,8,9 _
etc.
IC2
E
e
7812
- 78L12 or
.
IN
ETI COOKBOOK
LM340-T12
7812 or
LM340 T12
OUT
REF
IN yOU OUT
REF.
-i
RV2
500R
SET
ZERO
Fig.5.2. Linear capacitance meter. A unijunction transistor, Q1, is
connected as a relaxation oscillator with a frequency determined by
R1-C1. The frequency of oscillation in this instance is about 1 kHz.
Pulses of about 1 uS duration are produced across R4 each time
the UJT "fires". The resistance between b2 and b1 of the UJT reduces to a low value each time the emitter conducts. Much of the charge
stored in Cl is "dumped" across R4 for the short duration that the
c -b1 junction of Q1 conducts.
The narrow pulses across R4 drive the base of Q2 via R3, which
serves as a base -current limiting resistor. The pulses cause Q2 to
conduct for the same duration, that is, about 1 uS, and negative -going
pulses from the collector of Q2 drive the "trigger" input of the 555
timer, 1C1. This is connected to operate as a monostable in this
circuit.
13
Cl
330n
R1
22k
II
IC1/1
IC1/5
IC1/3
13
9
IC2/1
2
NOTES:
10
INPUT
POWER RAILS NOT SHOWN
IC1, 74CO4, PIN 14+5.6V
PIN 7
OV
IC2, 4030, PIN 14 +5.6V
I
+5.6V
R5
1M
+5.6V
OV
PIN
1M
R7
T22
7
OV
IC3, 4013, PIN 14+5.6V
PIN 7
OV
01, BC548
D1, 1N914
R2
RV1
100k
220k
'SEE TEXT
USE
OV
C5
100p
0V
R12
39k
C2
330n
R3
22k
IC1/4
IC1/2
IC1/6
I"CAL.
IC2/2
R10
3k3
R
REF.
INPUT
+5.6 V
R6
OV
1M
R4
R8
220k
1M
RV2
C4
22
100k
tIC3/2
OV
D S
c7.13
OV
91
IC2/3
+5.6V
470
LED
1
-AAM--110-0.
R14
10k
K
+5.6V
R15
10k
01
OUTPUT
0-1800
OV
C8
4u7
T
OV
OV
Fig.5.3. Phase meter circuit. The two inputs are first squared. For
example the reference input is amplified by gates IC1/2, IC1/4 and
IC1/6 and then applied to IC2/2, one of the spare EX.OR gates whose
other input is grounded. This conveniently behaves as a Schmitt
trigger type of bistable circuit. The average of the output of this gate
is formed by R8 and C4, and this is inserted via R6 as the DC level at
gate ICI /2.
This produces two important consequences. Firstly it forces the
output of IC2/2 to a symmetrical 180° on/180° off condition which
is kept stable by almost complete DC feedback. And secondly,
because we now have a true squaring circuit rather than a zero crossing detector, all errors due to even -order harmonic distortion are
cancelled. R4 and RV2 are used to adjust for input offset and set the
exact 180° condition.
IC gates IC1 /1, IC1/3, IC1/5 and IC2/1 process the signal from
the other channel in an identical manner, and the two squared outputs are fed to gate IC2/3 which is the gate that forms the EX.OR of
them. Its output is filtered by R11 and C6 and a voltage proportional
to the phase difference of the inputs may be taken from across C6.
for instance it may be
RV3 is used to set this to a convenient value
set to 180 mV for a 180° phase difference and read it on a digital
m ultim eter.
-
+ x--
SK1
SK2
R
+4 LEDI
+9V
1k0 2%
1mA
R4
10k2%
FSD
SW2
2
R5
9V
-NW`o
R6
T
7
100k 2%
IC1
3
1M_VW--
3
4
R8
4
R2
150
il FC1
R7
2k7
100p
560k
RV1
4k7
CAL
°
Sw1a
OV
C\SW1h
NOTES:
Q1 IS BC109
IC1 IS 741C
LED 1 IS TI L209
14
when the complementary outputs Q and Q have equal average values.
Secondly these gates can be arranged to turn the flip-flop on and off
to give a conventional phase meter circuit output. While this does not
give as accurate a reading, it does give one which is of opposite
polarity for leading and lagging voltages and which can therefore be
recorded graphically and unambiguously on an instrument such as a
chart recorder. This is therefore designated the recorder output.
R3
R1
2k7
201
5V6
In order to detect which of the inputs is leading the other, the
two voltages from the squaring circuits are also fed to the D type flipflop IC3/2. One voltage is used for the clock input and the other as a
data input. This type of flip-flop is really a data latch, and whatever
voltage is present at the D input at the moment when the clock
voltage changes from low to high is held until the next clock pulse.
Thus if the D input stays low until after the clock input goes high,
the output Q will always remain low showing that the D input lags
the clock input. The complementary output Q will be high and this
is used to turn on the transistor and LED indicating this lag condition.
Since any noise arriving at the clock input can cause spurious resetting
of the flip-flop, it is preferable to use a clean voltage to drive it. This
is why this channel has been designated the reference. Noise on the
other channel is almost completely ignored.
These then are the basic EX.OR functional parts of the phasemeter, and his would leave one flip-flop unused. In fact it turns out
that there are two functions that these gates can usefully perform.
First, for setting up the input squaring circuits: if the flip-flop is
slaved to the squaring circuit, the exact 180° condition can be set
Ì
T
9V
T -9V
Fig.5.4. (Left). Linear ohm -meter circuit. The circuit is divided into
two parts: a reference voltage generator and a readout unit that indicates the value of the resistor under test. The reference voltage
generator section of the circuit comprises zener diode ZD1, transistor
Q1, and resistors R1 and R2. The action of these components is such
that a stable reference of about 5 V is developed across R2. This
reference voltage is fed to the op -amp resistance -indicating circuit via
range resistors R3 to R6.
The op -amp is wired as an inverting DC amplifier, with the 1 mA
meter and R8-RV1 forming a voltmeter across its output, and with
the op -amp gain determined by the relative values of ranging resistors
R3 to R6 and by the negative feedback resistor Rx. RV1 is adjusted
so that the meter reads full scale when Rx has the same value as the
selected range resistor. Under this condition the op -amp circuit has a
voltage gain of precisely unity. Since the values of the reference
voltage and the ranging resistors are fixed, the reading of the meter
is directly proportional to the value of Rx, and the circuit thus
functions as a linear-scale ohm -meter and has a full scale value equal
to the value of the selected range resistor.
ETI COOKBOOK
FEATURE: Circuits
O
NOTES:
D1,2 ARE 1N4001
OFF
100KHz
SW1b
0-
IC1 IS 741
IC2 IS 555
t00Hz
R7
33k
SW1s 100kHz
GANGED
/
Cl
HIGH -
+
470n
10R1
-r
k
t
C3
5611
INPUT
C5
100
9V
-L-
LOW
O
R5
10k
R13
R6
+
1M0
R3
10k
RS
390R
22k
C2
10
R14
33k
t
M1
100uA
Fig.5.5. Linear frequency meter. The circuit consists of an op -amp
operated as a Schmitt trigger to amplify and square the input signal,
followed by a 555 timer wired as a monostable, giving a short output
pulse of fixed width for each cycle of input signal. This pulse drives a
moving -coil meter, the reading being an average of the pulse amplitude, which is proportional to the pulse frequency. As the pulse
frequency is directly related to the input frequency, the meter reading
is directly proportional to the input frequency.
330R
LEDI
5v
100R
K
100R
OK
4 k7
The input signal is coupled into IC1 via Cl, which provides DC
blocking. Protection from overload caused by high amplitude input
signals is provided by a diode clipper consisting of D1, D2 and Rl.
The diodes are connected in an inverse -parallel arrangement so that
both positive and negative peaks, above the diode forward conduction
voltage, are clipped.
The output of IC1 is a train of square waves at the same frequency as the input. The output of IC1 is differentiated to provide
short trigger pulses for the 555 timer, IC2. The differentiating network consists of C3, R7 and R8. This network is arranged to provide
a trigger pulse that is always shorter than the output pulse of the 555.
Capacitor C3 is selected to give the shortest possible pulse to the 555
consistent with reliable triggering.
The output of the 555 monostable will be a pulse of fixed width,
determined by the range resistors, R9 to R12, and capacitor C4. The
ranges are arranged to give a 75% output duty cycle at frequencies
of 100 Hz, 1 kHz, 10 kHz and 100 kHz on the input.
The output pulse from the 555 is clipped at 5V6 by a zener
diode, ZD1, to avoid inaccuracies caused by falling battery voltage
(as the battery ages). The meter responds to the average value of the
clipped pulses. As the frequency increases, the duty cycle (on/off
ratio) of the pulse train increases, increasing the average voltage and
thus the meter current in direct proportion. Thus the reading on the
meter will be linearly related to frequency.
5V
2k7
2k7
100R
C9--,AAA-0 0/P1
SPDD
100R
-
IC3d
I
O/P1
330R
LED2^
--0
IC2
2k 7
5V
100R
S
PDT
0/P2
,
1
0/2
IC4b
NOTES:
IC1 IS CD4049 CMOS
IC2 IS SN7404 TTL
IC3,4 ARE SN7400 TTL
ETI COOKBOOK
330R
LED3
/
5v
Fig.5.6. (Right). Sequential Logic Tester. Anyone testing a sequential
logic circuit requires input pulses free of contact bounce. This unit
does this, providing two switched, jitter -free outputs and a 'slow'
variable speed clock. The complements of these signals are also
provided.
The components shown give the clock a frequency range of
1-200 Hz. The clock's buffered output will drive up to two TTL
inputs.
The 100R resistors on all outputs provide some measure of
accidental short circuit protection.
15
300 WATT
AMP MODULE
For many applications there's no substitute for sheer power - low efficiency
speakers, outdoor sound systems, or maybe you like the full flavour of the
dynamic range of a high power amp. Whatever your requirement - this
'super power' module shduld fit the bill.
-fi amplifiers are becoming more
and more powerful, and with good
reason. Modern recordings, especially direct-cut discs, have a useful dynamic range approaching 40 dB between the
quieter musical passages and the peaks of
the crescendos. If the quieter passages are
played at at a power output of 100 mW,
which is not untypical in a domestic environment, to faithfully reproduce the full recorder dynamic range of a good record
without clipping the peaks would require
an amplifier capable of delivering 1000
watts! This, coupled with the current trend
amongst some manufacturers to build
speakers having quite low efficiency, plus
the number of people who like their music
loud (and undistorted) makes the case for
high power amplifiers very strong indeed.
Over the past six or séven years we've
had many requests for a high power amplifier. It would have been possible to design a
unit using a large number of readily available power transistors in the output - in fact,
one design used a total of 24 devices in the
output stage! Difficulties for the home constructor in this approach are obvious, regardless of expense.
For various reasons a bridge amplifier
was ruled out when the design of this amplifier was considered. Hence a plentiful
source of suitable output transistors was
first sought.
There are really not too many transistors available that meet the requirements.
Firstly, adequate safe operating area
(SOAR) is of prime importance. Next, and
probably of equal importance, is availability. Let's have a look at the SOAR problem
first. Some high power transistors don't
compare too well with the ubiquitous
2N3055 (and its complement, the MJ2955)
when operated as an amplifier. Take a look
at the set of curves plotted on the accompanying diagram. This compares the safe
operating area curves of a number of power
transistors. Operation of any power device
Hi
58
must be confined to the area inside the
device's curve at worst case. If the current/
voltage operating point is allowed to fall
outside the area of the SOAR curve during
any part of the operating cycle for the device, it will be destroyed - with amazing
rapidity. Now, the 2N3773 and MJ802
transistors have been around for some time
and at first glance would seem good choices for a high power amp, but note that
their SOAR characteristics are not much
better than the 2N3055. In fact, at 40 V
(Vcc) the MJ802 is actually worse. In contrast, the MJ15003 is quite a long way outside the curve for the 2N3055 and therefore has a much higher power rating when
used in an amplifier. Hence the MJ15003
and its complement - the MJ15004, were
chosen as the output devices for this
design.
ETI APRIL 1980
PROJECT
Another problem that arises with a design such as this is protection for the output
devices. Amplifiers using transistors such as
the 2N3055 can easily be protected with a
fuse. In high power amplifiers where
supply rails of 60 - 70 volts are necessary,
the energy available (from the filter capacitors) will easily destroy the transistor and
the fuse - in that order. The answer is to use
electronic current limiting in the output.
This adds complexity, but is cheap insurance against accidental (or deliberate!)
abuse. The curve showing the limiting
effect on the SOAR characteristics of the
Mil 5003 for the protection network used
in this amplifier is shown on the diagram
with the other SOAR curves.
-. IIII_ I
0.6
0.5
0.4
0.3
VER
ES P(OW RROUTzWT
92
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9.04a,9.03\
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OHM LOAD
IlliFr
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10
POWER (WATTS(
@ 19
B
OHM LOAD
100
200
300
Hz
Output Cost
The main cost of the amplifier is in the
output stage, transformer and heatsink. We
therefore decided to go to a slightly more
complex input stage to improve the performance. This type of amplifier usually uses a
Class A driver which introduces second
harmonic distortion. By using a complementary-differential input circuit we have
been able to eliminate the Class A driver
and therefore kept the second harmonic
distortion very low indeed. The distortion
curve shows the distortion is well under
0.1% until almost full power output. The
'bump' in the curve around the watt is the
point where the output stage changes from
Class A (peak output being less than the
bias current) to Class AB operation.
The complete amplifier, including the
power supply components and the output
transistors, is assembled on a single PCB.
An aluminium bracket holds the output
transistors conducting heat from the output
stage to the heatsink. Only three sets of
external connections are made to the PCB:
input, output and power supply AC input
from the transformer.
Construction
Start the construction by making the
aluminium bracket. We used two length of
3 mm angle. This bracket is 3 mm thick and
two must be placed back to back to make
the required 6 mm thickness for adequate
thermal conduction to the heatsink assembly. If you elect to use a Philips 6 5D6CB
heatsink (see the box on 'Heatsinks'), a
single 6 mm thick angle extrusion can be
used, fixed to the flat side of this heatsink.
Heatsinks
There are several alternatives you can
choose from for heatsinking the amplifier
output stage. The heatsink shown was
made from sheet aluminium and has a thermal rating of 0.55 C/watt. This is the rating
we recommend for any heatsink if the amplifier is to drive a four ohm load, particularETI APRIL 1980
ly for pop group use. If it is driving an eight
ohm load in typical domestic use, half the
fins may be left out (every second one)
resulting in a thermal rating for this heatsink
arrangement of 0.75 C/watt. Use 1.6 mm
thick aluminium sheet - certainly nothing
thinner. A heatsink with about 1 C/watt
rating and substantial fan cooling is another
alternative.
Remember that dissipation in the heat sink will be about 200 watts at full power
output. That means a temperature rise of
110 C above ambient if the amplifier is run
continuously. Poached eggs anyone? Temperature rise with music or intermittent use
is considerably less, of course, as average
power dissipated is much lower.
'
\
SAFE OPERATING AREA (SOAR) FO
SOME COMMON TRANSISTORS
AMP
377
2
Ilk.
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á
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M
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Above and right: operating characteristic of the 300W module circuit.
100
VOLTS
SPECIFICATION
Power output
8 ohm load
4 ohm load
Frequency response
200 watts RMS
310 watts RMS
20Hzto20kHz
±0.5 dB
Hum and noise
re 200 W into 8 ohm
-105
dB
Input sensitivity
8 ohm load
1
V for 200 W outpu
4 ohm load
1
Total harmonic
distortion
see
Damping factor
20 Hz to 3 kHz
5 kHz
10 kHz
20 kHz
65
55
45
35
V
for 300
W
output
graph
BUYLINES
Most of the components used in. the 300 W
power amplifier module are standard and
readily available. The output transistors
(types M j 15003 and Mi 15004) are available
from Macro Marketing Ltd. If you don't
feel up to making the heatsink shown,
Maplin can supply a suitable heatsink
type 60ÚN (order code YB26D).
The power supply transformer and
capacitors may prove a little more elusive.
If you are unable to find the 2500u 80 V
types, you can use 100 V capacitors mounted off the board. The transformer specified
is a high power type, which you may have
-
to
have wound to order. Several firms
advertise a transformer winding service in
the classified sections of electronics publications. Shop around for the best price.
Trent Transformers will supply the transformer for E16.95 plus postage.
Macro Marketing Ltd.,
396 Bath Road,
Slough, Berkshire.
Tel : 06286 4422.
Trent Transformers Ltd.,
26 Derby Road,
Long Eaton, Nottingham.
Tel
:
06076 66716.
59
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ETI APRIL 1980
PROJECT:300 WAmp
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insulating
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Exploded view of how the TO3 output transistors are assembled to the angle brackets.
Below: Component overlay for the module.
.
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IN
ETI APRII. 1980
PROJECT:, 300 WAmp
PARTS LIST
RESISTORS
R1,3
R2,10,14
R4
R5,27,34
R6,7,17,18,
All
23
4k7
22R
2k2
22k
10k (6k8 for 4 ohm loads)
R8,9,15,16
R11,13
R12
R19
R20,25
R21,24
R22
R26
R28-33
R35,36
R37-42
R43,46
1
1/4W,
10k
220R
390R
6k8
100R
100R 1W
Powering Up
The set of output transistors are expensive to replace. Therefore, we recommend
you follow this test procedure in the interest
of conserving supplies of same.
The power supply AC input should be
connected to the transformer (see the overlay) but no power applied. You'll need a
multimeter of at least 20k ohms/V
sensitivity.
2.
3.
4.
5.
6.
7.
Remove the two fuses.
Soldera small link across C11.
Solder a wire between this link and
the ouput pad.
With no load connected and no input
signal, switch the power on.
Check the supply rail voltages. These
should be about 68 volts each (plus
and minus).
Check the voltages on the cathode of
ZD1 (should be about +37 V) and the
anode of ZD3 (should be about -37V)
with respect to 0 V.
If these two voltages differ with respect
to each other by a volt or so, check
other voltages around the input stage
ETI APRIL 1980
Q7
Q8
130140
BC549
Q9,10
BD139
Q11
130140
Q12,13
Q14,15
Q16
Q17
MJ15004
MJ15003
80140 or BC640
BD139 or BC639
1N5404
1N4004
D1-D4
D5,6
5V1 300 mW
62 V 5W
SV1 300 mW
Z D1
Z D2
Z D3
MISCELLANEOUS
see text, PCB, Transformer
Heatsink
300W), 4 fuse clips, 2 x 5A
(47 + 47V
SEMICONDUCTORS
8C547
Ql-Q3
Q4-Q6
BC557
220R 5W
0.1 ohm, 5W
39R
test.
1.
CAPACITORS
C1--4
250uu 80 V electrolytic
CS
2u2 35 V tantalum
C6
330p ceramic
C7
100u 25 V electrolytic
C8
330p ceramic
C9-11
100n polyester
C12-14
1n5 polyester
100n polyester
C15-17
k0 5W
to spread under compression and finally
tighten all nuts. Last of all insert 08. Smear
the inside of the hole it sits in with heatsink
compound to ensure good thermal contact.
Now you can solder all transistor leads.
Check the component placement
against the overlay now, just to ensure all is
in order. If you wish, you can test the amplifier up to the driver stages for correct operation before assembling the the unit to the
heatsink. Remove the fuses before applying
AC input from the transformer. Refer to the
'powering up' procedure. If there are any
problems, look for errors in component
placement or orientation - particularly with
diodes. If all is well, assemble the module
to the heatsink and you're ready for the big
4R71W
POTENTIOMETERS
RV1
2k2 trim
1OR
1
5k6 1W
R44,45
R47
5% unless noted
kO
-
fuses.
14. Measure the voltage drop across one
of the 10 ohm resistors placed across
the fuse holders and adjust RV1 to give
a reading of 1.0 V.
15. Switch off, allow the filter capacitors to
discharge and remove the two 10 ohm
resistors. Replace the fuses.
16. Connect suitably rated loudspeakers,
warn the neighbours, connect a signal
source to the input (turn down the volume), switch on the power and put
the amp through its paces.
At this stage we'll leave the applications of this module up to you. No doubt
to determine the reason.
8. Check the DC voltage on the output
(with respect to 0 V). It should be within 20 mV of zero.
9. Inject a sinewave signal into the input
at a level of about 20 mV (RSM). Don't
use a higher input level. Output should
be 1 V RMS.
10. Switch off the main power and allow
the filter capacitors to discharge. Remove the input signal.
11. Solder a 10 ohm 1/2W resistor across
each fuse holder. Rotate the trimpot
RV1 so that it is set at maximum resistance. Remove the short across C11
and the link from there to the output
pad.
12. Switch on
if the 10 ohm resistors
immediately vaporise you either have
a short or some fault in the output
you have plenty in mind already.
We are preparing a follow-up article
for a later issue in which we may cover
such things as pre -amps, bridge operation,
design parameters and variations etc.
Keep reading.
stage!
13. If all is well, check the DC output voltage. It should be near zero.
ETI
HOLES MARKED A 4.5mm DIA
Below: heatsink bracket metalwork details.
HOLES MARKED B 3mm DIA
HOLES MARKED C TAP 4BA OR 4mm DIA
ALL OTHERS 4mm DIA
MATERIAL 40 x 12 x3 ALUMINIUM ANGLE EXTRUSION
152
22
52
82
nz
+-I
142
-c
o
12
33
66...I
47
87.5.4 99
e
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40
20T
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+6
115.5 127
T31,5
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2
OPPOSI.E HANDS
9.5
21
37.5
49
61
71
83
97
110
,
125
135
145
MICROFILE
We've seen hide nor hair of Henry Budgett, since he took delivery of two
new machines. He's finally returned to the land of the living with his reports
on the new HP85 and Microtan systems and more besides.
Two months may only be eight weeks to you but to someone in
here it has been a very packed time. Certainly in terms of the
home and personal computer market it has been a very fast
moving time indeed. Owing to a wide variety of reasons last
month's offering never reached your waiting eyes so some of the
news may be a little less than fresh - it is slightly less than boring,
though.
This
is really a preview offering. shall be dealing with at least
two of these machines again, probably devoting a whole month to
each. The first two are now well known, but have been fortunate
I
I
enough to have one of a very limited quantity of the top system for
review and
The Dream Machine
The reason most people give when asked why they chose a PET
that it is a complete unit; VDU, keyboard and mass storage all in
one small unit. Whilst this new system from Hewlett Packard has all
the previously mentioned parts and a thermal printer as well it
resembles a PET in about the same way as a racing car resembles an
MG; they are of the same genus but the HP is so far advanced that it
outstrips almost anything in the personal computer market. This is a
personal computer and not a home machine. Why the difference?
Well, with some few notable exceptions, the home computers
is
currently available are overgrown programmable video games, not
that that in any way detracts from their worth. This has been
designed for research laboratories, education and other serious
users who will be able to benefit from the superb range of facilities
that are offered.
Basically, the HP85, for that is its name, consists of a single
box, slightly larger than an Apple, with a 5" VDU, tape cartridge,
thermal printer/plotter and full ASCII, numeric and function keyboards: Inside is a complete custom designed system. For example,
the CPU card consists of the custom built CPU, four ROMs holding
32K of BASIC/operating system, eight RAMs (16 K of dynamic)
controlled by yet another custom built chip, the keyboard controller (again custom) and finally the bus driver chip which is, quite
naturally, custom built. Grand total is sixteen chips! The VDU has a
totally independent memory of four screens-full that can be scrolled
or copied direct to the printer at any time or under program control.
The graphics capability is excellent with an available by
points. Program access is simple, you can manipulate scales and
put labels on graphs and diagrams. To make life a little easier for the
user the built in plotter turns diagrams on their edge for printing, this
allows continuous strip charts to be produced.
Finally on the hardware side we have the tape system. This is
mechanically the same as that used on the HP minis but unfortunately the format has been slightly changed. The method used is
Hewlett Packard's new HP85
(right) is a powerful machine in
a compact package and at a
reasonable price.
The Atari 800 (far right), one
of two new Video Computer
Systems on their way.
66
ETI APRIL 1980
MICROCHIPS AT MICRO
PRICES
Compare our prices before you buy
elsewhere. All brand new, prime.
DISPLAY LEDs AT
LOWEST PRICES
NEWS: Digest
99p
99p
DL704/DL707
500/FND 510
,FND
MEMORIES
2102 Static RAM
80p
2114 Low power high speed 300NS
4.00
5.95
3.95
3.95
4116 Dynamic RAM
5101 1K CMOS RAM. Low power
Low power
EPROMS
3.75
5.95
19.95
1702A
2708
2716 Single 5V supply
2.98
3.98
AY -5-1013A
AY -3-1015
ErMKOMZEMIll
4.50
RO -3-2513 UC
r
FLOPPY DISK CONTROLLER
1771 Single Density
IBM Compatible
FD 1791 Dual Density
IBM Compatible
SUPPORT DEVICES
39.95
Ideal for DMMs, DPMs,
7.97
digital thermometers,
AM/FM radio readouts.
7.95
Just look at the features.
ARE
Compare our prices below distributors!
5.95
CL7106CPL
6.95
CL7107CPL
2.95
CL8038CCPD
18.75
16.75
80p
CM7216AIJI
CM 7216BIPI
CM7555IPA
LINEAR ICs
NE555
NE556
RC4136
SN76477N
TL071
TL074
TL081
TL082
TL084
17p
40p
747
25p
748
LM301AN 25p
LM318
LM 324
LM339
LM380
LM 496
LM3900
1
42p
70p
35p
35p
60p
60p
45p
18p
50p
90p
1.95
40p
1.30
35p
80p
1.10
TL490. New 1.75
XR2206 3.00
XR2207 3.75
7805/781255p
7905/791265p
78HO5SC 5.75
78HGKC 6.25
AY 3'8910
osah9e4-9
ee $-ere
three note chords, make bangs, whistles,
sirens, gunshots, explosions, bleets,
whines, or grunts. In addition, it has
provisions to control its own memory
chips with two IO ports. The chip requires
+5V @ 75ma and a standard TTL clock
oscillator. Atruly incredible circuit + VAT.
Only £8.95 + VAT W /Basic Spec. Sheet
(4 pages)
60 page manual with S-100 interface
instructions and several programming
examples £1.95 extra.
Texas Instruments
Low Profile Sockets
8 PI
P111$
16 PIN
18 PIN
22 PIN
n,
`1`ií7
40 PIN
Kit
NEW
The SE -01 is
contains all
the parts to
build a pro-
a
complete kit that
e
sound effects
generator.
Designed
around the
new Texas
Instruments
SN 76477
Shell Kit
board
provides
Gof
banks
MINI
of
DIP
switches and
pots to program
the
various combinations of
the
SLF
One
Shot,
and Envelope Controls. A Quad Op Amp
IC is used to implement an Adjustable
Pulse Generator, Level Comparator' and
Multiplex Osdillator for even more versatility. The 3'/a"x 3" PC Board features a
prototype area to allow for user added
circuitry. Easily programmed to duplicate
Explosion, Phaser Guns, Steam Trains,
or almost an infinte number of other
sounds. The unit has a multiple of applications. The low price includes all parts,
assembly manual, programming charts,
and detailed 76477 chip specifications. It
runs on a 9V battery (not included). On
board 100MW amp will drive a small
speaker directly, or the unit can be connected to your stereo with incredible
results! (Speaker not included.)
COMPLETE KIT ONLY £12.50
P&P 50p + VAT
Ordering information: For orders under
£50 add 50p p.&p. Add 15% VAT to
total. All items are subject to prior sale and
therefore subject to availability. Prices are
subject to change without notice.
Price
.07
.09
10
15
18
PIN20
22
24 PIN
28 PIN
Sound Effects
SE 01
VCO, Noise,
PROGRAMMABLE
SOUND GENERATOR
The AY3-8910 is a 40 pin LSI chip with
three oscillators, three bmplitude controls,
programmable noise generator, three
mixers, an envelope generator, and three
D/A converters that are controlled by 8
BIT WORDS. No external pots or caps
required. This chip hooked to an 8 bit
microprocessor chip or Buss (8080, Z80,
6800 etc.) cap be solftware controlled to
produce almost any sound, it will play
14
Intersil 7106 ND 7116.
Oscillator,
-tweet
Contacts
ratio, wide viewing
angle, rapid response,
proven sealing techniques, superior MTBF,
reflective aluminium foil.
Over 300,000 already
sold! Perfect interface for
the
35p
400V 5a
AY3.8910
Ultra low power con-
Sound Chip,
UNIVERSAL SCR
ezeNt
I
grammable
VOLTAGE REGULATORS
C 106 D
time there was
a Mr Slaymaker whose factory in Esher was almost completely destroyed in a fire. While
tiptoeing through the ashes, Mr
Slaymaker found his telly - hanging chain broken from the intense
heat, case badly distorted, front
panel non-existent and full of waOnce upon a
ter from the firemen's hoses. After
a few months Mr Slaymaker unwelded the controls and plugged
it in. Using a hacksaw for an
aerial, he obtained a near perfect
picture. There's a moral there
somewhere. If you're intending to
burn your house down round
your ears during crossroads
should get hold of a JVC Video sphere colour telly pretty quickly.
sumption, high contrast
Due to bulk purchase we are able to offer
unbeatable prices on INTERSIL CHIPS.
30p
33p
Fireside Viewing
decimal points and
"LO BAT" indicator.
DOWN
709
723
741
1.24 25+ 100+
LCD106 6.45 5.50 5.25
.5" Field effect LCD display featuring 31 digits,
colon, plus/minus sign,
19.95
MC14412VL
KEYBOARD ENCODER
AY -5-2376
CHIPS
iLiiiiayl
3
FD
INTERSIL
THE MOST VERSATILE
LIQUID CRYSTAL DISPLAY
.22
.25
.28
fTlicro
circuits
4 Meeting Street
Appledore, Nr. Bideford
North Devon EX39 1 RY
Tel. Bideford (02372) 79507
Telex 8853084
yourself
a
circuit diagram
for a metal locator? Construction of the PCB's no problem, but
if the tantalising treasure -tracing
tit -bit doesn't come as a complete
kit, where do you get your hardware from. At worst, you can end
up using plant pot saucers to
house the search coil and broom
handle (complete with splinters)
for the shaft.
Fear not - Sonasonics comes
to the rescue. They can now supply a metal locator shell in kit
form from £17.25 including VAT
and carriage. The kit includes a
search coil case, shaft, handle and
a case for the electronics. The
case can be supplied drilled or
undrilled, if requested.
Further details from Sonasonics Electronics, 11 Park Road,
Ashford, Kent TN24 8LU.
GIVE YOUR HOME -BUILT METAL
DETECTOR THE PROFESSIONAL LOOK
Now available,
a complete kit of parts to house your detector, comprising high quality
black A.B.S. vacuum formed 101/2" square head halves, vacuum formed top
case assy all the anodised metal tubing fully adjustable, and injection mouldings
screws etc, order as kit. S.E.1 Price only £17.25 inc. VAT.
.
Also available, with pre -wound and set up head assy with head module, for T.R.
metal detector, complete with circuits and application notes to produce your own
I.B. /T.R. unit. Order as kit. S.E.2. £23.50 inc. VAT.
Kit S.E.3. Comprises of kit 2 but with P.C.B. and components to produce a three I.C.
three transistor metal detector with meter and audio output, inc. everything you
need, high quality meter and headphones, etc. Only £39. 95p inc. VAT.
All the above kits are carriage paid.
SPECIAL OFFER TO "ETI" READERS £1 OFF THE ABOVE KITS ORDERED
BEFORE APRIL 30th.
Components available for building your own designs, S.A.E. for lists of parts.
SONASONICS ELECTRONICS
11a PARK ROAD, ASHFORD, KENT, TN24 8LU
TEL. 0233 35871 (24 answering service)
13
NEWS
similar in many ways to a soft sectored floppy disc; you have a
directory which is searched for your required program, this is then
located and loaded. The speed of this operation is considerably
faster than that of the conventional cassette.
Super Software
The HP has tucked away inside its diminutive frame the best
version of BASIC that I have come across on a micro. It meets, and
often exceeds, all the latest ANSI standards for this, much abused,
language. I strongly suspect that anyone who had been brought up
solely on a Microsoft type implementation would get severe brain
damage! In fact this BASIC has everything you could wish for, and
it's logical too. For example, you get renumbering, full error checking programmable user keys, full debugging, single stepping, optional screen (DISP) or printer (PRINT) displays, or both... the list goes
on and on.
One of the most common complaints about home produced
software is that it isn't 'bombproof'. Well I've written more than a
few on the HP and you can protect them very easily, even to the
point of securing your files on the tape so that no-one can list or edit
them.
A possible moot point is that, to quote any of my rivals in the
game, 'HP do not even say what processor the 85 uses'. As you may
have guessed I'm talking about machine code, and as mentioned
earlier the HP has a custom chip. Not only did someone not read
their press release carefully they also didn't listen when it was stated
that an assembler will be available soon! Anyway you don't really
need machine códe as in the main this machine will be used as an
instrumentation controller, or as a system to analyse results produced by other systems.
In Brief
There you have it, unfortunately in brief form because of a lack
of white space to fill, but the HP 85 has arrived, bringing with it a
whole new generation of professional computers that are cheap
enough to be dished out to each member of a research team. I said
'cheap enough', it does cost £2000 but this price is artificially high yUrct 3oe
Iogersetl
they can't make enough to go round - and it is quite possible that it
will fall to around £1200. If that happens it could well clean up the
micro market overnight. After all, people are generally prepared to
pay for quality! (My thanks are due to the team at HP who let me
keep the system until they lost all hope of ever seeing it again!)
Video Strikes Back
Ingersoll, the watch people who expanded into electronics
recently, are to distribute the Atari 400 and 800 Video Computer
Systems in this country. Information is scarce at the moment, but it
appears that the top model, the 800, will be equipped with 8K RAM
- expandable to 48K - and 8K ROM - expandable to 40K. CPU is the
trusty old 6502 and the system will handle four floppies and has a
full feature ASCII keyboard with programming being done in Atari
Basic. Prices will range from £400 to £750 approximately and
features such as full colour and sound are standard. For more details
watch this space.
The Odd One
Whilst making one of my occasional tours around London's
Computer shops came across a familiar sight. There, sitting on a
service bench, was what appeared to be a 32K, large keyboard PET.
However, on closer peeking it turned out to be something rather
different. It had a full terminal style keyboard. Some of the keys had
I
been moved to more sensible places (such as the cursor controls)
and there were no graphics legends on the keys. What was it?
Simple really, it's the PET Business Machine. Owing to the fact that
some of the RAM had expired I couldn't see it going but apparently
the lower case, that you normally have to POKE out, is available and
you have to POKE the graphics if you want them. A very sensible
idea really, but this machine had an American transformer so I
decided to track down some details. Commodore say that they are
not yet available in this country but they are planned to arrive in the
near future, a few months but that's their estimate.
If you are planning to set up a business system with a PET in the
driving seat I reckon this would be much better and easier to use
than having graphics floating about. If anyone out there has one or
knows more about it please drop me a line and give me your
impressions.
Lh:ce.nr.5c'.
Tone Deaf
Regular readers may remember that wrote a piece on modems not so long ago. Well, Microfile bears fruit occasionally, we
are going to publish a design in the march issue of Computing
Today, but just for those of you who want to go your own way here
is the standard frequency set for data transmissions.
I
ETI
US Standard
!
ftJ11NNt41tí(U:Glìl;ki
lüüìCdthl!H11111p
CCITT Standard
,
Mark
IG/r.'l
1270 Hz
Originate
Chan.
Space
1070 Hz
Mark
2225 Hz
Answer
Chan.
Space
2025 Hz
Mark
980 Hz
Space
1180 Hz
Mark
1650 Hz
Space
1850 Hz
1
2
being produced in PCB form by ZOT
Engineering Ltd of Bogpark Road, Musselburgh, Lothian. Naturally
it uses the above frequencies and runs at 600 Baud.
CTs modem project is
ETI APRIL 1980
67
NEWS: Microfile
Sinclair's ZX80
-a Tiny BASIC machine in every sense.
reduced to a single digit number. It is very restricted, as you would
expect, on data processing functions like string handling and because of the design the CPU has to produce all the functions of the
system, hence the blurring of the screen when a program line is
entered. Each line is syntax checked on entry at the bottom of the
screen before it is allowed to move up and join the others at the top,
an unusual feature on small systems.
Overall the new Sinclair has very interesting possibilities, and
at £99.95, inclusive of VAT but not power supply, it does represent
one of the cheapest entry points to high level programming.
With no facility for machine code, and not much mention
was made, so one presumes, that the MK 14 will continue to
support this area of the Sinclair market. In my humble opinion this
machine will be excellent for education on the mass scale but once
people have had a taste they may well find that they cannot expand
enough to meet even moderate needs. Still, as the executive toy for
1980 its success is assured.
Further design restrictions have meant that you can only add
an extra 16K of RAM onto the unbuffered bus. These expansions are
-in 3K blocks for which you pay £12 for the board and a further £16
per K of RAM. Talk was made of adding new ROM sets, masking the
board, new extras like languages, disks, etc but as the CPU is
already rather overworked somewhat doubt the practicality of
these ideas.
is
I
And Now For The News
So much for last month's delayed offerings, here is the news. As
most of you will probably be aware Britain's enterpreneur extraordinaire, Clive Sinclar, launched his new micro onto the british
public in a blaze of TV and Press publicity. Called the ZX80 (well it
uses a Z80 so why not) it s about the smallest home computer with
built in BASIC yet, you could even call it hand-held. have not yet
received a sample for review but when it comes in I'll take a close
look. Here, however, are a few observations from the launch and
subsequent perusal of the handbook.
Based on the Z80A, running at 3.25 MHz to save timebase
dividers, it has a sealed, touch sensitive keyboard which offers
single key programming of most BASIC functions. say most because this is really only a Tiny BASIC but it has been squashed even
further by use of a look -up table system where each command word
I
I
Orange Blossom
From the stable that brought forth' the Tangerine VDU system
about a year ago now comes a new micro system called the
Microtan. This is an excellent kit, also available ready built, that
sells for a mere £69. It offers an excellent start in 6502 based
systems. have built one up in the last week, it worked first time,
and would seriously suggest that if you feel unsure about soldering
on double -sided, plated-thru boards you buy the ready -built system. It is not a beginners' kit; spent over an hour and a half
soldering and I'm no novice, but what you get at the end is really
worth all the trouble.
The monitor is one of the best 1K versions I've come across in
quite a while and the concept is excellent. Basically at this stage you
need a five volt power supply, the Microtan and a hex keypad to
start on the machine code. However, if you want a full ASCII you
can plug it in place of the hex pad - the monitor actually works out
which type you are using. Many people will make comparisons
with the Acorn. Both are low cost 6502 -based kits, but the Microtan
gives you a VDU, rock steady I'm glad to say, right from the start
with optional graphics and lower case rather than a sub-calculator
type LED display.
Expansion is by a way of second board called Tanex, cunning
names these, which gives you an extra 7K RAM, 6K ROM, 8K
Microsoft BASIC, cassette I/O and enough general purpose parallel
and serial 1/O to get most of you frothing at the mouth. And, believe
it or not, both cards are on PCBs not much bigger than a Eurocard.
Further expansion is by way of a 40K, yes that's forty, RAM board
and a disk board which will offer up to four units. Not only is the
I
I
I
cost extremely reasonable but the design hasn't been skimped. In
the days of Britain -Knocking dare one even say that Microtan will
probably knock the (expletive deleted) out of the lower end of the
market and possibly make at least one other UK firm look to its
laurels in haste? will be presenting a complete Microfile on this
gem at a later date so keep your ears on.
I
ETI
Microtan
68
- an excellent introduction to 6502 based systems.
ETI APRIL 1980
PROJECT
PROGRAMMABLE
TOUCH DIMMER
A sophisticated multi- function touch -controlled lamp dimmer
with built-in memory and a few other special features.
lamp dimmer project
does away with the usual on/off/dim
control knob and replaces it with a
single touch -sensing pad or switch. The
touch pad is coupled to a sophisticated IC
which processes touch -duration information and then controls the brilliance of the
lamp (via a track) in accordance with that
This unsusual
information.
If the pad is simply touched for a brief
period (60 to 400 mS) the lamp merely
changes state; ie, from OFF to ON, or vice
versa, depending on its previous state. A
longer touch (greater than 400 mS) causes
the lamp brilliance to cycle slowly from
dim to bright or vice versa for the duration
of the touch, taking about seven seconds to
span the full brilliance range: when the
touch is removed the prevailing brilliance
level is 'remembered' and maintained indefinitely. At switch -off (a brief touch) the
chosen brightness level is stored: this
brightness level is set again at switch -on
(another brief touch). In the case of dimming, control starts from the stored value.
Remote Control
The dimmer unit can be controlled
locally either by the touch pad already
mentioned or via a simple press -to-close
switch. Additionally, however, the unit is
provided with a pair of 'extension' pins
which enable the unit to also be fully controlled by any number of remotely positioned switches or touch-pad modules. All
control points work in the 'OR' mode.
The touch dimmer circuit uses the
'hum pick-up' principle of touch detection
and is specifically designed to operate with
'modern' house wiring in which the lamp is
connected to the Neutral side of the mains
and the on/off switch (or dimmer) is connected to the Live side. The basic dimmer
circuit can, however, also be used in 'old'
house wiring systems, in which the lamp is
The ETI Touch
Dimmer is designed
to fit into a standard
plaster -depth lighting
switch box. The
triangular touch plate
from Maplin gives the
project a professional
finish.
ETI APRIL 1980
connected to the Live side of the mains and
the switch is connected to the Neutral, but
in this case the unit must be activated via
push-button (rather than 'touch') contacts.
In either case, the circuit can be used to
control up to 300 watts of lamp power.
Construction & Use
Our prototype unit is designed to fit
into a standard plaster -depth lighting
switch box. Before starting construction,
check the project's suitability to your existing wiring by making an accurate cardboard cut out of the PCB and checking that
it will fit comfortably into an existing lighting switch box. If all is Well you can proceed with the construction.
Construction calls for a certain
amount of care. Note that the capacitors
are miniature types (see Buylines). Components L1 -Cl and R10 are RF interference
suppression components. L1 consists of
approximately 50 turns of 0.5 mm enamel copper wire, wound on the body of
Cl.
When construction of the PCB is complete, connect the unit to the mains via a
suitable lamp in accordance with the circuit diagram and the overlay and give the
unit a functional check via the touch pad
lead. Check that the unit dims and turns on
and off as already described. Also check
that it does not cause excessive interference
on your radio set: if excessive interference
is experienced, try reducing the value of
R10 to 47R.
When you are satisfied that it is operating correctly you can fit the PCB and the
touch pad (see Buylines) to a standard
blanking plate (available from your local
electrical shop) as shown in the photos. The
plate is provided with a central 'knock-out'
hole. Open the hole, push the touch pad
through the plate hole and the central hole
on the PCB and bolt the two units firmly
together. Now connect the touch pad to the
PCB touch pin via a solder tag and nut.
Finally, check that the holes on either side
of the PCB line up with the securing holes
of the blanking plate.
71
TOUCH
LAMP
PAD
B
r
R1
1k0
1W
NOTES:
C2
D1 IS 1N4001
Q1 IS TRIAL TIC206D
220n
400V
02
IS
BC182L
IC1 IS SIEMENS S566B
TOUCH DIMMER
b
L1
(SEE
TEXT)
EXTENSION
SWITCHES
02
8
Q1
R10
100R
TOUCH
PAD
SA
4M7
IC1
R4
1M5
MT1
4
5
2
3
o
C4
100n
400V
PB1
470p
Cl
o
C5
R2
10k
BC212L
47n
T
L
O
O
RI
I
SB
L
Fig.1. Circuit diagram of the dimmer.
PARTS LIST
When you finally fit the completed
unit into its switch box take care to ensure
that no short circuits occur. You can cover
vulnerable components such as Li with
insulation tape if you wish. When fitting the
unit; note that the box's earthing lug
should, in most instances, be at the Ci -C2
corner of the PCB.
If you decide to fit extension switches
to the unit note that the connecting leads
carry live mains and normal safety precautions must be taken.
NOTE: The S566B IC used in this project is a special-purpose touch
dimmer device manufactured
by Siemens and must not be
confused with the similarly
numbered NE566N voltage
controlled oscillator IC.
RESISTORS
Ri
1k01W
R2
R3
R4
10k
120R
R5,6
RT,8,9
470k
4M7
100R
Rî0
1M5
CAPACITO RS
Cl
C2
C3
C4
C5,6
150n 400 V polyester
220n 400 V polyester (see
Buylines)
100u 25 V electrolytic
470p ceramic
47n (see Buylines)
SEMICONDUCTORS
IC1
55668 Touch Dimmer
TIC 206D
Q1
BC182L
Q2
BZY88 15V
ZD1
ZD2
BZY88 18V
1N4001
Di
MISCELLANEOUS
MK blanking plate, touch pad, 2 -way ter50 turns of
minal block (2A rated), Coil
0.5 mm enamelled copper wire on Cl.
-
-
L1 is wound on Cl
50 turns of 0.5 mm
enamelled copper wire. As an additional
safeguard, a turn of insulating tape keeps
it out of harms way in the box.
72
ETi APRIL 1980
PROJECT: Touch
Dimmer
HOW IT WORKS
Most of the 'intelligent' action of the circuit
is carried out in special-purpose P-MOS
integrated circuit ICi. This IC receives
instructions via a touch pad or touch switch.
to be varied from roughly
maximum via the triac.
mation and then does or does not send
appropriate gate drive pulses to lamp switching triac Q1 via pin 8 and current booster transistor Q2.
high peak drive power (1.2 watts), their
MEAN power dissipation is very low (about
12 mW). This power is derived from the
mains via RI-Ci-ZD1-Di and C3 and is
delivered to ICi and Q2 as a smooth 14
volts DC from 'reservoir' capacitor C3. This
method of operation is only made possible
by the fact that the triac is not gated on
until at least 30° after the start of each half
cycle, thereby enabling C3 to attain and
maintain a virtually full 14 volt charge
throughout each half cycle. The IC logic
operations are synchronised to the zero crossing points of the mains signal via the
It processes the input touch -duration infor-
If the IC decides that the lamp should
be switched on it sends one 30 uS, 100 mA
gate pulse to the triac in each mains half
cycle (every 10 mS), at some phase -delayed
time after the start (zero -crossing point) of
each half cycle. The magnitude of the phase delay determines the brilliance of the lamp:
if the triac is triggered shortly after the start
of each half cycle (short delay) the lamp
burns brightly: if it is triggered near the
end of each half cycle (long delay) the
lamp burns dimly. The maximum anddninimum phase delays are limited to 150 and
30° respectively, enabling the lamp power
3%
to 97% of
Although ICi and Q2 generate relatively
intended for genuine 'touch contact' use
and works on the high -impedance hum pickup principle. The touch pad is effectively connected to the mains live terminal
via high -value resistors R7 and R8, which
limit the touch pad currents to safe and
minimal levels. ZD2 limits the pin 5 'hum'
signal amplitudes to safe values.
The pin 6 input is intended for use with
push-button touch switches or with any
number of parallel -connected 'extension'
switches. The extension switches can either
be normal push-button switches or 'touch
switch modules', each comprising one
transistor and three 4M7 resistors connected
as
shown.
R4-C4 network.
'Touch' information can be fed to either
pin 5 or pin 6 of ICi. The pin 5 input is
The dimmer can be used with lamp
loads up to 300 watts. Li and Cl and the
associated resistor are RFI-suppression components.
+ll lt!lIBNI
BUYLINES
Due to miniaturisation certain components have been selected for
their physical size. These are C5, C6 and C4 and are Siemens type
B37448, which are available from Electrovalue. C2 has also been
carefully chosen. This capacitor is an ERO type MKC 1864 and can
be obtained from Watford Electronics. The following companies
stock the S566B touch dimmer- Electrovalue, Watford Electronics
and TK Electronics. An anodised touch plate which can be purchased from Maplin Electronics gives an attractive appearance to
the completed project.
All the other components should not prove difficult to
obtain from major stockists advertising in this issue.
Fig.2. (above left). This is how you fit a quart
into a pint lighting box. Q1 is mounted flat
on the board to save space. Note the
orientation of C3.
The PCB fits neatly into its box (above). If
you have any bits sticking out, you've done
it wrong!
ETI
ETI APRIL 1980
73
RAVEN ON ...
Jet -setter Dave Raven of Metac Electronics reports on his latest trip
(purely business, of course) to Hong Kong, complete with holiday snaps
indication that Hong Kong is overcrowded came as
the aircraft made its final approach to the runway. Washing
billowed from the network of multi-storey buildings which
appeared almost close enough to reach out and touch. Kai Tak
Airport is situated on the side of Kowloon Peninsula with its runway
projecting out towards Victoria Harbour. The giant Jumbo hurtles
itself down between the skyscrapers and races out towards the end
of the runway, which of course is surrounded by water. Reminding
myself that the pilot must have done this many times before and that
it would be extremely unlucky for this particular aeroplane to
overshoot, nestled down into my seat and thought about how
many times the stewards had demonstrated putting on and inflating
the life jackets. The sweet placid smile of the Singapore Air hostess
hadn't cahnged throughout the landing, which I had monitored
continuously knowing that tell -tale signs of trouble would first
appear there.
The first
I
Street Life
If Hong Kong can survive the effect of its massive over population then the future growth of their electronics industry looks set to
follow the same pattern as Japan. If the Government could somehow restrict any poor quality products leaving the country as happens in Japan by subjecting all exports to independent quality
checks, then the effect of this would up -lift their whole product
image.
Hong Kong is split into two main parts - Hong Kong Island,
which is the original British Colony, and Kowloon, which is on the
mainland tip of China. Kowloon is the controversial part of Hong
Kong and also the adjoining New Territories which are on lease to
Britain until 1999. The site of so much construction and land
reclamation must infer that no one is particularly worried about the
likely outcome of events when our lease does run out. A new multi
million pound underground railway system has just been opened.
Motorway sections, bridges, flyovers and a road tunnel under the
harbour increase your confidence that the British expect to be here
for some time yet. On occasions I found it necessary to remind
myself that this was, in fact, still a British colony, since the life style
was certainly different from any other have seen. How much a part
of Britain the Chinese felt, just could not gauge. I did, however,
notice when walking around the Chinese districts of Mong Kok that
most of the corner street players, strange fortune tellers with caged
birds and story tellers had a lot more common with say Pekin than
with Manchester.
I
I
While
Wait
U
The other area in which we differ is our capacity for work.
Never before have been so amazed at the speed in which things
can happen. All readers must have heard tales of the Hong Kong
tailor-made suits. Well, can confirm they are true. In just three days
which included Saturday and Sunday my colleague and I had a suit
made to measure and three shirts each. This included a fitting of
course which all took place in our hotel rooms. This story will of
I
I
76
course inflame the wrath of clothing manufacturers in this country
who will try to make me feel guilty by pointing out the rate at which
companies that manufacture suits are going out of business. While
feeling genuine sympathy I cannot help feeling that it takes a little
more than sweated labour to be as efficient as the Hong Kong
Chinese. Wage rates are generally regarded as good and working
conditions are not dissimilar to those have seen in many British
factories. A visit to the East End of London will demonstrate this
point, particularly the little clothes manufacturers off Middlesex
Street (Petticoat Lane). My admiration for the tenacity of the Chinese
in building up such a prosperous country in an area about the size of
Leicester is tremendous. The contribution which has been made by
our own Government deserves praise too when one considers that
the whole country is administered by British Civil Servants.
Visiting the industrial area of Hong Kong is an experience in
itself. This must be a unique environment of multi-storey blocks of
factories containing more people than I think I have ever seen.
Walking through the little street markets during the lunch hour (they
do have one), I can only describe it as similar to trying to traverse the
crowds at Wembley Stadium on Cup Final Day. As part of my brief
was to discover the source of the Digital Watch it was with much
trepidation that I entered the factory blocks. Travelling up in a lift
with about three times as many people as I would think was safe, I
hesitantly made my entrance. Where were the rows of children
assembling my watches? No sign of malnutrition or overseers lashing the workers to produce more.
I
Swiss Watches - Chinese Style
am afraid to report to the sceptics of Hong Kong products that
was only confronted by modern UK style offices with splendid
clean modern production lines, manned by rows of pretty healthy
looking girls who were carefully assembling the products. Rows of
computerised automatic bonding machines were churning out
watch modules and automatic computer testing was being carried
out on a million pound computer system. The design engineers,
quality assurance managers and factory managers were all highly
competent people whose only crime against the workers of Britain
is a high level of job satisfaction and a level of productivity that we
can only hope to aspire to. One of the companies visited has a
complete in-house design capability so forget the stories that all the
products are ripped -off from American or British designs. This same
firm is building a new factory to give them their own wafer fabrication plant which reduces their reliance on American chip manufacturers. Stainless Steel, mineral glass watches, water proofed to three
hundred atmospheres are soon to be typical specifications coming
out of Hong Kong. Some of these companies are now approved to
Swiss Watch Industry standards and to prove it some well known
names are being assembled here. Hand held games are to be very
important products this year, probably as big as the early TV Game.
Models to watch out for are the LCD varieties with little stick -figure
football players that dart about on the display. These nay not be
ready this year in the UK but this has to be the start of a flat screen,
LCD hand held television.
I
I
-
ETI APRIL 1980
NEWS
Rural Smells
No visit to Hong Kong can be made complete without visiting
the New Territories, and this rural part of Hong Kong must be very
similar to Main Land China (only 22 miles from Hong Kong). We
travelled to the China border on a train full of young Chinese youths
off on a Sunday outing. The journey took about two hours due to
delays caused by trains coming from the opposite direction loaded
with ducks, cattle, pigs, sheep and also armed guards at the rear. In
the station these trains were halted along side our own train and
with the windows down the smell managed to ruffle our normal
calm British decorum. The houses in the rural areas are still very
small by our standards. was amazed to see how every available
patch of ground was beautifully cultivated and tangerines were
being grown in pots for part of the New Year celebration. The China
border is not too impressive, but then how could it be, with
just open fields and a twisting road leading off into the distance.
With binoculars you could just make out the guards at the border
and was amazed to see a few people wandering across carrying
shopping bags. later learned that they live on the border and are
free to cross into Hong Kong but clearly prefer to go back to China.
must confess that had an urgent desire while standing there, to
walk off down the road and discover if there really are nearly one
billion people living over those hills all capable of being as industrious as the 5.5 million on the side was on.
I
I
I
This computer is used at Elcap Electronics in Hong Kong for automatic
testing of watch chips.
I
I
I
Arab Solar Energy
While in Britain we rapidly use our scant supplies of oil, energy
'conscious Arabs in the Middle East are investing millions of pounds
in conserving their own. The future of solar energy looks very
promising according to a report published by the political editor of
Middle East Magazine. The arab world receives solar energy equivalent to an average of 275 watts per square meter. With a land area
of over 11.5 million square kilometers and assuming that only one
percent of this could be utilised for solar energy collection, a total of
over 30 billion megawatts is potentially available. This could be
converted to usable electricity at an efficiency of at least 10 per cent
producing over 3 million MW or the equivalent of 3000 large
power stations, generating 1000 MW each.
Automatic wire bonding of watch modules at Elcap.
SOLERAS
Large scale solar projects are under way and include a 1.5
million dollar solar -powered heating complex for a massive air
force school that is being built at Tabuk. It involves 4370 sq. m. of
solar collectors and is being built by an American firm on subcontract. By far the biggest project undertaken to date is the
SOLERAS programme with the USA. On the American side the
Department of Energy has set up an agency, the Solar Energy
Reasearch Institute (SERI), run by the Mid West Research Institute in
Colorado.
Most effort so far has gone into building a 350 kW solar power
station near Riyadh using photovoltaic cells to supply electricity to
ETI APRIL 1980
two villages. Plans are also under way to build a desalinating plant
and contracts will shortly be awarded for this work. By introducing
greenhouses into agriculture, Jordan has increased its production of
cucumbers and tomatoes fivefold, especially in the winter. Perhaps
the most spectacular innovation has been the construction of a solar
powered emergency roadside telephone system. most major roads
now have such phones and the director of the Jordan Telecommunication Corps is investigating the possibility of introducing solar
powered television sets to remote areas (he obviously hasn't heard
about Sinclair's Microvision).
ETI
77
TOMORROWS
OFFICE?
Take a step into the future at the Design
Centre. Ian Graham reports on time travel in the Haymarket.
If you find yourself within visiting distance of London's Haymarket
between now and March 8th, it's worth popping into the Design
Centre. They've collected together a handful of exhibits to show
what the office of tommorrow might be like and they've called it
'Tomorrow's Office Today'.
The typewriter has been the office workhorse since granny was
knee-high to an abacus, but two boxes of tricks on display may well
see it off the the scrap heap - the Supertyper word processor and the
Microwriter.
Box No.1
The Supertyper FD85 word processor takes much of the repetition out of typing. When visited the show, a demonstration of the
I
FD85 had attracted a small crowd of exhibitionists (or do mean
exhibition goers?). Corrections or major alterations to typewritten
text usually means retyping. Not so with the word processor. The
letter that needs an alteration can be displayed on a screen above
the keyboard. Then, at a touch of a button or two, words or letters
can be added or deleted, columns can be shifted, lines ruled,
paragraphs moved and so on ad miraculum. When the boss is
happy with his words of wisdom, the processor can print out as
many copies of them as he wants in his favourite type face.
If you have to send out a few dozen standard letters, the
processor can print them out, adding a different name and address
to each.
I
Box No. 2
If you're working away from the office and you want to make a
few notes you could reach for the nearest scrap of paper or use one
of those pocket cassette recorders. The scrap of paper stands a good
chance of getting lost and the cassette recording has to be transWhen you hear that spine -chilling word
80
cribed on your return to the office. How about giving a Microwriter
a try?
Five Finger Excercise
The Microwriter is about the size of a large pocket calculator,
but it only has six keys (five plus control). These can be used in
various combinations to enter letters (upper and lowercase), numerals, punctuation and all the other normal keyboard symbols.
The text is displayed as you write it on a twelve character LED
display, moving from right to left. There is also an optional TV
display for sixteen line read-out and editing.
The control functions let the operator read or jump forwards
or backwards and allow instant editing - the deletion or insertion of
letters, words or even complete paragraphs.
Microwriter's memory can hold 8,000 characters (about 1500
words) in RAM and further storage is possible by means of microcassette.
The contents of the memory can be printed out when you
finally get round to calling in at the office or it can be transferred to
micro -cassette for playback later.
When the Microwriter is plugged into its automatic, high speed
printer, your notes are transferred on to paper at up to ten times the
speed of your best secretary. Each printer can handle between ten
and fifteen Microwriters.
Now meet SUE, designed by Tom Stout and on show for the
first time. Sue is an automatic draughtsman. The hardware includes
a display screen, a plotter and a disc memory system. The drawing
and the typewritten additions from the keyboard are shown on the
display. When the drawing is satisfactory SUE can transfer the
display on to paper. If your paper copy of the drawing is lost or
damaged or needs further alterations, don't worry - the original is
still stored on the disc memory.
- time - and have to toddle back to the office, the Logatel phone aid showsyou
who's been trying to call you.
ETI APRIL 1980
FEATURE
The several -secretary-power Supertyper word processor system takes the repetition out of office paperwork.
Phone Bugs
Minster Automation would love to come and bug your phones.
It's worthwhile, though. Their Tiger Cub telephone management
and accounting system records the length, cost and distance of
outgoing calls and the number of incoming calls that go unanswered. What good is that? Well, Tiger Cub can identify under-used
extensions which you could do without. All the recorded information can be printed out if necessary.
Call Again
When you ring an extension on your internal phone system for
the sixth time and no-one answers, the atmosphere can start to go a
bit blue. Why waste all that time and effort dialling and hanging on
the end of a deserted extension? Instead of regularly ringing back,
why not just ring once and let the phone do the rest? If your system is
fitted with the Logatel aid, you can ring once, wait for the tone that
begins when the phone is left unanswered and then dial your own
number. When the phantom phoner finally returns to his office,
Logatel can display the numbers he has to ring back - yours among
them. Logatel is manufactured by Feedback Ltd of Crowborough.
First Class Chips
16 lines at a time from Microwriter (above) can be displayed on TV.
The silicon chip has even got into the post room. Although
your accounts department and your company records may be
computerised à la space age technology, is your post room staffed
by little old men in frock coats using a steam franking machine
under one of Edison's original light bulbs? Mailtronic's postal
weighing device is aimed at you. You put your letter or package on
top and touch the finger sensitive keys for postal zone, class of post,
registered post, etc and the chip in Mailtronic uses all the information to compute the correct postage. When there's an increase in
postage, all is not lost. You just change the chip.
Push-button postal charges from Mailtronic.
ETI APRIL 1980
a Tiger Cub on your phones (above) or Euro
(below).
Put
C
your accounts
81
FEATURE: Tomorrows Office
Once you've mastered Microwriter's keyboard (right) you can happily tap in up to
about 1500 words, without a tape recorder
or reams of paper. Like everything else,
mastering the keyboard alphabet (shown
below) is just a matter of practice.
Alphabet
mPouxï'd
i
A
b
oó
°o
ó°
ö
Ç
ï°
- °° /J
oo
o.,0
`,
®
00
° 9
..m-
o°q
O
-
..o.m
0
o
óIó
,,,40-
d00
°
'.
°
i
pO°
POy,
0.0r
°L-L
Q
Q
,
°v2
ü
0
0 0
/o%
Q9
g
o
°'
-
q,
0p}¡/
®
O
.Q
o
:_i
°
0
cy0
m
O°Oo
o
o
,
.......,.. P......<."e.....
Instant Accounts
hours to get all the sheets in the right order. The Watkiss all-purpose
EuroC is a British -made desk-top microcomputer system designed to handle a corhpany's entire accountancy procedures at
low cost. It is capable of being operated by staff without any
computing or accounting knowledge. Produced by Eurocalc Ltd of
London, with hardware form Plessey, the system can store up to
12,000 transactions per month for 1,000 clients, so it is particularly
suitable for small to medium sized companies. Each daily purchase
or sale is entered via the keyboard on one of eight standard 'input'
forms displayed on the screen. As each form is completed, the
computer automatically updates the firm's records. Every month a
set of management accounts can be printed out. Necessary reports
can be printed out at any stage.
Paper Mill
If you have several thousand sheets of paper and you need to
assemble sets of notes from them, it could take your Girl Friday
collator could do it for you and much quicker (it doesn't have to
stop to powder its nose). It can handle a wide variety of material at
the rate of 45,000 sheets per hour.
The Film Business
When you keep some of your records on microfiche, reading
them can be a bit of a strain on the eyes. Take the load off your
lenses with the Alpha microfiche reader from CAPS Microfilm of
London. It will magnify the sheet of film to an easily readable size.
The reader has a special grid index plate with a moveable pointer to
select a particular page in seconds.
Seeing Is Believing
Many of these exhibits are demonstrated from time to time.
You can try some of them out yourself. If you want to know when
your favourite box of tricks is going to be demonstrated, give the
Design Centre supervisor a ring on 01-839 8000 ext 309.
Ell
Firm Finding
SUPERTYPER LTD
33 Lower Combe Street
MINSTER AUTOMATION LTD
Stone Lane
Croydon CRO 1AA
Tel: 01-680 3477
Wimborne
Dorset BH21 1HD
Tel: 0202 880251
MICROWRITER LTD
7 Old Park Lane
London W1Y 3LJ
Tel: 01-493 5633
TOM STOUT & PARTNERS
6 College Avenue
Formby
Merseyside L37 3JJ
Tel: 07048 74266
82
FEEDBACK LTD
Park Road
Crowborough
Sussex TN6 2QR
Tel: 08926 3322
MAILTRONIC LTD
300 Neasden Lane
London NW10 OAD
Tel: 01-450 7535
EURO-CALC LTD
55-56 High Holborn
London WC1
Tel: 01-405 5223
WATKISS AUTOMATION LTD
Holme Court
Biggleswade
Bedfordshire SG18 9ST
Tel: 0767 313853
CAPS MICROFILM LTD
7 Westmorland Road
London NW9 9RG
Tel: 01-204 4111
ETI APRIL 1980
NEWS: Digest
CALCULATORS
MCC Preamp (Jan)
SCIENTIFIC
enquiries about
he power supply for the
Moving Coil Cartridge for use
with the Audiophile System 4000
project. You don't have to build a
separate supply. The MCC Pre amp will run happily from the
We've had
*SPECIAL OFFER
TEXAS T159 together with PC 100C
(Complete as manufacturer's specifications)
£285.00
TEXAS/HP Accessories available
*TEXAS T159 (Card prog 960 prog steps of 100 mem)
*TEXAS T158 (Key prog 480 steps of 60 mem)
*TEXAS PC100C (Printing Unit for T158/159)
Prog Steps)
*TEXAS T157 (Key Prog 8 mem. 150 Keystrokes/ 50
£158.50
£60.00
£140.00
£25.00
For your Thaw T1158/ 59 Calculator
ELECTRICAL ENG. MODULE
LEISURE (GAMES) MODULE
STRUCTURAL ENG. MODULE
15-0-15 volts System 4000
preamp supply (see ETI Oct 79).
If you're just building the MCC
Preamp and not the complete system, then have a look at ETI
October 1979 for details of the
15-0-15 supply.
Foiled,Again
NOW AVAILABLE
*TEXAS TI PROGRAMMER (Hexadecimal Oct)
*TEXAS 7151 /iii (10 mem 32 Prog Steps Stat/Sci)
TEXAS T150 LCD (Sci/Stat. 2 Con Mems)
TEXAS T125 LCD (Sci/Stets)
TEXAS T53 (Sci. 32 Prog Steps -Coa Mem
+80
,
Prog List Applications book)
£46.50
£26.30
£23.00
£17.00
£25.00
Make more of your
Tetras T158/69 Calculator
MATH/UTILITIES MODULE
for you! Most programs in this library
If you write your own programs this library is
or as subroutines of your programs.
are designed to be used either on their own
formatting and large-scale
Applications range from utility programs such as printer
plotting to advanced mathematical routines.
Module includes:
Superplotter. Sorting. Data
Prompter. Alpha Messages. Printer Fomatting.
Factors. Hyperbolic Functions. Gamma/a
Prime
Arrays. Data Packing.
Interpolation. Roots of
Factorial. Random Numbers. Normal Distribution.
Equations. Discrete
Function. Minima*. Romberg Integration. Differential
Module Check.
Fourier Series. Calculator Status. Variable Arithmetic.
£90.00
*TEXAS T158 with Maths/ Utilities
£ 186.50
*TEXAS T159 with Maths /Utilities
£80.00
*TEXAS T158 with Applied Statistics
£305.00
*TEXAS T159 with PC100C & Applied Statistics
SPRING SALE
spec. master module,
*TEXAS T159 Calculator (complete as manufacturer's
set of 40 Blank Prog. Cards with
charger, etc.). PLUS statistics module and extra
wallet, etc.
ONLY £180
NEW TEXAS T158C*
mem even when
*Continuous program facility on all 480 Program steps/60
£79.50
calculator switched off
*TEXAS T158C (complete plus Applied Stats. Module)
*TEXAS T158C + PC100C
£99.00
£208.00,
£50.75
*1-IP33E (8 mem. Pro Sci/Sta)
£40.50
*HP32E (Advanced Sci with Statistics)
£188.70
*HP67A (K Prog 224 Steps 26 Mem)
£384.35
Printer)
with
*HP97A (Fully prog
£173.48
H P41 C (the newest calculator from HP)
£27.73
,
CASIO FX8000 (10 dig Sci/Sta. Stop Watch /Alarm)
£47.50
CASIO FX501 P (Sci. LCD Prog. 128 Steps 11 Mem)
£65.00
22
Mem)
256
Steps.
Prog
CASIO FX502P (Sci. LCD
for
recorders
permits Progs to be recorded on to standard cassette
CASIO Prog Adaptor
POA
later
stage
at
replay on Casio FX501 P/Ex502P
.
-
LEXICON LANGUAGE TRANSLATOR
French/ Italian /German /Spanish etc)
(With 6 Lang. Module
-
£128.70
NOW IT'S YOU AGAINST 'COMPUTERS'
£76.50
CHESS CHALLENGER "7" (7 Levels of game)
beginner to Master Plus) The strongest Prog yet in
CHESS CHALLENGER "VOICE" (10 Levels
160,000 bits
twice as fast as the other challengers. A microprocessor with 126,000 to
this series
opening & end game solutions.
of read only Mem. Over 8000 bits of Random Access Mem. Teaches
and in addition IT SPEAKS. Complete with Deluxe
Plays against itself. Solves book problems etc
POA
playboard, hand carved men with magnetised base plus Deluxe carry case
ideal game for learning)
COMMODORE "CHESSMATE" (8 levels 32 International openings
-
-
-
*FREE
-
-
£50.
- mains/Charger included*
LEARNING AIDS
TEXAS DATAMAN (Number Games -Table learning etc. 5/10 yrs)
TEXAS SPELLING 8 (Spelling Games ideal 5/10 years)
TEXAS SPEAK AND SPELL (for older children 8/13 years)
£18.00
£22.50
£39.95
IDEAL FOR STUDENTS
ALL WITH LCD DISPLAY
TEXAS T120 (Jun Sci + Con Mem)
TEXAS T135 (Sci /Stet C Mem)
Min Sec)
TEXAS T138 (Sci/Con Mem-Polo Rec Cony Dec Deg cony/Deg
CASIO FX3200 (Sci/Scat 10 Dig)
£13.00
£17.00
£19.95
£19.00
arel Components have announced a new range of thermofoil heaters designed and
made by Minco Products, the pioneers of etched foil heater tech-
nology.
The flexible, chemically
etched foil heater elements are laminated between thin insulating
layers to provide a uniform or profiled heating pattern. Applica-
World-beater
HA12017 is
Hìtachi's new
claimed to be the world's
lowest noise audio preamp IC.
The Hitachi silicon surface process ensures that the exceptionally low noise characteristic is remass
in
repeatable
liably
production.
So you want to see sóme
figures. Under standard pick-up
conditions, a S/N ratio of 82.6 dB
is achieved, with an equivalent
tions? Temperatures of everything
from inertial guidance systems to
batteries, baths and ovens can all
be controlled.
For a complete temperature
control system, foil or wirewound
sensors can be integrated with the
heater element for more accurate
temperature control. For further
details contact Carel Components
Broadway,
40-44 The
Ltd,
Wimbledon SW19.
input noise of just 0.185 uV.
Moreover, the IC has less than
0.002% THD over the audio
band (20 Hz to 20 kHz) at an output level of 10 V rms (under RIAA
conditions). The SIL package provides maximum isolation between stages.
If you're just dying to design a
preamp round the HA12017 you
can get hold of one for £1.57 from
Ambit International, 200 North
Service Road, Brentwood, Essex
M14 4SG.
15%)
GOODS FULLY GUARANTEED PRICES EXCLUDE VAT (ADD
Company/ Hospital and Governmentorders accepted by phone
Barclaycard/Visa /Access accepted by phone
TEL. 01-455 9823
r
EXPORT ORDERS WELCOMED
Air Freight/Air Post Delivery
Quotations on request
L
MOUNTAINDENE
,22 Cowper St., London, EC2
ETI APRIL 1980
15
FEATURE
TECH TIPS
Boat Heater
Thermostat
B.
Kongstad
When thethermistor Rlsenses it
is
start the heater it is essential that the relay
pulls distinctly even if temperature falls
slowly. The heater must be on till temperature has risen by at least 2 C, otherwise it
has to start and stop too often. The desired
Schmitt action is achieved in the following
way. When temperature falls the resistance
of the thermistor increases and the comparator at pin 6 triggers the flip-flop. Then pin
3 goes high and pulls the relay. At the same
time pin 7 goes low. Resistor R6 shunts the
lower part of the 5-5-5 k voltage divider
and this helps the comparator to give a
definite trigger for the flip-flop.
If the thermistor is replaced by an LDR
the trigger action will take place when it is
1
NOTES:
R3 IS 50k -200k
TH1 IS THERMISTOR 1k3 at 25
D1,D2 ARE 1N4005
time to
R4
(SETS TRIGGERIN
TEMPERATURE)
sufficiently dark. By this means a riding
light can be lit at dusk when at anchor and
the light turns off at dawn. But don't use
50 Hz incandescent or fluorescent light
when setting the sensitivity. Your eye will
not sense the flickering but the LDR does.
o
+9
Cl
-15V
100n
R3
33k
4
03
C2
100n
04
TOUCH
PLATE
RI
R2
10M
R5
12k
2k7
14
10
3
1
08
12
13
IC1d
IC3
11
010
0
11
0
1
D1
12
NOTES:
IC1 IS 4001 OR 4011
IC2 IS 4024
IC3 IS 4066
CLOSED
09
8C109C
IC2
1N4148
NORMALLY
Q1
13
R4
1k2
NORMALLY
OPEN
02
-Ve 9-15V
o
One Contact
Touch Switch
G.N. Durant
The switch is operated by stray mains hum,
connected to the touch plate when briefly
touched. The hum is coupled to the input of
ICi a (used as an inverter) via R1 (a low pass
filter). The output of ICi a is not sufficient to
operate the final stage, so it goes through a
Schmitt trigger (ICI b,c). Once the trigger
output starts to change, R3 provides the
trigger for a rapid change.
IC2 is a seven stage ripple counter. Q1
is driven from the output of the seventh
stage via R5 (current limiter resistor). C2
and R4 reset IC2 at switch -on so the outputs
are all low and the switching transistor is
off. When the touch -plate is touched, IC2
will receive a 50 Hz signal. At pin 3, the
logic state changes every 64 pulses, switch-
ing Q1 on and off. The plate is touched
until the desired state is obtained and then
released.
Ql sends a pulse through to IC3, a solid
state CMOS switch. This can be fed via an
inverter if desired. The switch must not be
used at more than its supply voltage - up to
15 V. The 'off' switch resistance is about
1013 ohms and the 'on' resistance is about
80 ohms at 15 V VDD (at 9 V VD,J it is 120
ohms99
Tech -Tips is an ideas forum and is not aimed at the beginner. We regret we cannot answer queries on these items.
ETI is prepared to consider circuits or ideas submitted by readers for this page. All items used will be paid for. Drawings should be as clear
as possible and the text should preferably be typed. Circuits must not be subject to copyright. Items for consideration should be sent to ETI
TECH-TIPS, Electronics Today International, 145 Charing Cross Road, London WC2H OEE.
ETI APRIL 1980
87
FEATURE: Tech Tips
__
R12
270R
:
Ll
+12V
(@2 mA)
R7
R4
47k
3k3
R6
R10
4k7
47k
RV1
L
500k
C5
330u
C3
5u0
Q2
BC169
)
BY
PASS
o)
OUTPUT
BYPASS
R8
SW1a
o
SW16
2k7
+
R1
R11
56k
47k
C4
INPUT
R9
1k5
R5
56k
100u
OV
o
/7777
Transcendent 2000
Preamp
R.N. Johnson
If this preamp is connected between the
External VCF Audio Input socket and some
musical instrument such as a guitar, then
the output from the synthesiser will consist
of the guitar sound modified by the synthe-
siser's VCF, mixed with the normal output
of the synthesiser. The preamp is necessary
because the VCF requires about 1 V to
work, but most guitars produce only 10-20
mV. The voltage gain needed is about 36
dB. Most other musical instruments should
also work as long as they have a pick-up
which produces about 10 mV or more
(even a microphone works and produces
some pretty weird noises). The level controls of the synthesiser and the preamp can
necessary.
O
SW1
Magnetic Light Dimmer
be used to determine the mixture of synth/
guitar in the output.
The circuit itself is suitable for low or
high impedance microphones/guitars and
RV1 varies the gain from about 10-36 dB.
The power supply of the synthesiser can be
used and the preamp will easily fit inside
the cabinet of the synthesiser (near socket
SK6 but away from the mains leads). The
switch is provided to bypass the preamp if
R1
L
10k
T. Hopkins
SW2
R2
47k
R8
A
partialsolutionto theproblem of leaving
lighting on unnecessarily is to have a resettable timer in place of a switch. However,
The choice of delay is difficult, particularly
when the room may be used continuously.
Ideally, it should be impossible to leave
the room without turning out the light. One
solution, shown in Fig.
is to build the
circuit into a wall box and carry a small
magnet on a keyring. When the magnet is
120R
%W
1
270k
1
placed over the reed switch, the lights are
turned on and, if the circuit is mounted on a
steel front panel, the magnet will stay in
place for as ling as is required.
The magnetic dimmer shown in Fig. 2
allows a choice of six different light levels
depending on which reed switch is operated. The resistor values shown were chosen
to suit the available triac. Other triacs may
require changes to some of these values.
The reed switches used measured approximately 1.125" and were mounted on
a piece of tinplate with epoxy resin (Fig. 3).
The front was then covered with a thin layer
of plastic. A magnet of 1/2" diameter was
used to operate the dimmer.
ETI APRIL 1980
SW6
8A 400V
C3
47n
600V
TRIAL
(INTERNAL DIAC)
R6
390k
R7
C1
10k
C2
100n
100n
250V
250V
LOAD
(UP TO1kVV)
N
220R
E
O
3A
400v
REED SWITCH
SW1
TRIAC
LOAD
(UP TO 50014/1
N
89
FEATURE: Tech Tips
o
+9V
Audio Display
R1
RV2
2M2
2k2
C.S. Histed
01
AC128
o
This circuit is a novel LED display, which
when plugged into your hi-fi will send a dot
of light zooming around a ring of LEDs at
different speeds, depending on the music.
The input signal from your hi-fi is fed into a
voltage controlled oscillator (IC1), which
then sends its variable length pulses to the
clock input of a 4017.
This causes each LED in turn to be briefly lit and, because the clock input changes,
the time taken for the dot of light to move
along the LEDs varies in time with the
music. The best visual output is achieved if
the LEDs are arranged in a circle of about
11/2" to 2" in diameter.
The input voltage can be adjusted by
the 100k preset and the normal speed of the
INPUT
RV1
IC1
100k
R2
1k0
R4
10k
Cl
150n
o
0V
NOTES
LEDS 1--10 ARE TIL209
IC1 IS NE555
IC2 IS CD4017
01 IS AC128
4
IC2 CD4017
10
CODE
1
KEY
15
61
32 3
33 1
22
33 2
76
22
33
76
00
34 6
01
336
SUM 6
RCL6
02
03
04
05
06
07
08
09
10
35
Yx
16
17
18
19
30
85
2nd
20
=
INV Yx
21
-35
05
85
5
=
-49
36
34 6
INV 2nd INT
2nd PAUSE
SUM 6
11
61 0
SBR 0
12
13
32
1
STO
61
1
SBR
14
32 2
1
1
STO 2
Electronic
Travelling Dice
1
15
5
6
10
9
13
LEDS
1-10
TIL209
leds can be adjusted as desired using the
2M2 preset. The 4017 is able to drive the
LEDs directly and no current limiting resistors are needed.
LOC
3
NE555
22
23
24
SBR
1
RCL 1
x t
RCL 2
2nd x t
x t
RCL 3
2nd x t
GTO
51 5
25
26
27
28
29
30
333 7
39 4
GTO 6
2nd LBL
86 5
39 4
86 6
56
5
RST
00
0
-R/S
RST
71
2nd LBL 0
X
01
42
43
44
45
46
47
48
2nd PRD 4
2nd LBL 6
2nd DSZ
71
86 0
55
41
5
V V
81
40
RCL 7
2nd PRD 4
51 6
31
32
33
34
35
36
37
38
39
1
STO 3
3
V
V
00
85
32 5
49
-61
86
35
=
STO 5
2nd INT
1
INV SBR
2nd LBL 1
5
RCL 5
-49
61 0
-61
0
INV 2nd INT
SBR 0
INV SBR
Vdd
CLOCK OSCILLATOR
1G
M.G. Argent
The heart of the unit is the 4017 divide by n
counter, IC3. The outputs in turn give a
logic level (+9 V) with each clock pulse.
To divide by six as required by a dice, the
seventh count (output six, confusingly) is
connected to the reset (RST) input. This
resets all outputs to logic 0 and the count
starts all over again ad infinitum.
So long as the clock enable input is
connected via the 10k resistor to VDD, the
count carries on as normal. If it is connected to 0 V the counter stops and remains in
the state it was in at that time. This is achieved by a normally -open push switch which
acts as the SPIN switch. When the switch is
operated it stops the counter.
Vdd
1
ETI APRIL 1980
OA
BO
O O O
C
OF
D
A
R3
10k
13
E
GO
SPIN
SWITCH
GND
1
6
ONO
NOTES
IC1 IS 4049
IC2 IS 4025
IC31S401]
SATT SUPPLY 9 VOLT
GND
GND
GND
`\
R4
1kO
Vdd
91
ANALOGUE
SWITCHING
Tim Orr, ETI's man of a thousand and one circuits, presents another
of his astounding features. This time his subject is analogue signals.
How to switch and with what.
There are many electronic functions that need to be able to turn
off and on analogue signals just as they would be by conventional mechanical switches. The relay used to perform that task
but it has almost entirely been superceded by electronic analogue
switches. The relay is still in use but it is now generally used to,
handle heavy voltages and currents. A small version of the relay, the
reed relay (Fig. 1), still has many advantages that have not yet been
r_o
overcome by electronic technology, these being very low contact
resistance, virtually zero noise generation and distortion and almost
total isolation between the control and switching section.
These features make the reed relay an ideal switch for high
quality audio signal routing. The device drawbacks are, that it is
physically large, heavy, expensive, consumes considerable power,
is susceptible to vibrations and generates interference.
r - -
SIGNAL
INPUT
--I
LIGHT TIGHT BOX
LDR
INPUT
10k
L
+5
CONTROL
SIGNAL
OUTPUT
ON/OFF
CONTROL
SLOW ATTACK AND DELAY
+5V
OFF/ON/OFF
CONTROL
Fig.2. A light dependent resistor can be used to make an analogue
switch.
Fig.1. A typical reed relay.
47k
Ios
INPUT
OUTPUT
CONTROL
+5V
100k
CHOPPING
TRANSISTOR
OV
_J
i
ON/OFF/ON
VGS
GOING
-Ve
INPUT
RON = LW
CONTROL
OUTPUT
--
Fig.3. A transistor chopper, often used to
turn off an analogue signal.
18
for
DI
LINEAR REGION
WHERE THE FET
BEHAVES LIKE A
RESISTOR (Ros)
VGS = OV
Fig.4. N -type FET characteristics.
J
TI APRIL 1980
FEATURE
However, as Vcs
Dependable Resistor
A simple electronic analogue switch can be made from a light
dependent resistor (Fig. 2). When light from the LED shines onto the
LDR, the resistance drops from a few meghoms to a few hundred
ohms. The device generates very little distortion and noise and is
thus suitable for routing audio signals.
The response time of the LDR is very slow, sometimes taking
100 mS to switch, it is both relatively expensive and large and it
consumes a large LED current. The transistor chopper, (Fig. 3), is
often used as a simple device to turn OFF an analogue signal. This is
done by turning ON the transistor and driving it hard into saturation, which in turn shorts the signal to ground. The transistor chopper is often used in organ and electronic piano circuits to produce
audio tones by chopping the envelope waveforms with squarewaves generated by a tone divider network. It is not easy to use the
bipolar transistor as a floating switch, as most applications require
but the JFET lends itself readily to this purpose. The characteristics of
a JFET (Fig. 4) show that in the region where the curves pass through
the origin the device is behaving very much like a voltage controlled resistor.
When Vcs is O V, the curve passing through the origin is at its
steepest, the FET having at this point its lowest Drain Source resistance (Ros), known as RON. This is typically a few hundred ohms.
is increased negatively for an N type FET, the slope
resistance increases until the pinch off voltage is exceeded. The FET
is then PINCHED OFF' and the effective Ros is typically a few
hundred meghoms. The JFET can be used as a variable resistance
device changing from a few hundred ohms to a few hundred
meghoms in times much shorter than a micro -second. This, combined with smallness of size, low cost, low power consumption, a
very high impedance at its control input and the ability of the drain
and source to float, makes the JFET an ideal analogue switch.
The series switch (Fig. 5) passes the signal with very little
attenuation when the FET is on and stops the signal when the FET is
off. There is a small stray capacitance (a few picofarads), between
the drain and source and this causes high frequency breakthrough
when the switch is off.
The shunt mode shorts the signal to ground when the FET is
turned on (switch off). The attenuation in this mode is R/RoN which
requires large values of R to get a large attenuation. To get the
advantages of both types of arrangement, a series/shunt switch can
be constructed using two FETs (Fig. 6).
When a FET switch is rapidly turned on there is often a click
generated, partly as capacitive breakthrough from the gate and
partly as an abrupt amplitude modulation of the analogue signal.
This can be greatly reduced by band limiting the gate voltage (C2,
R3) and by removing any DC component from the analogue signal
(Fig. 7).
STRAY CAPACITANCE
INPUT
OUTPUT
BF244B
O
INPUT
ON
*
OFF
REMOVES DC 'THUMP'
10k
INPUT
12V
OUTPUT
OUTPUT
10M
OFF
ON
-12V
ON
-6-717\43/
Fig.5. The series switch (top) passes the signal when the FET is on
and stops it when the FET is off. The shunt switch (above) shorts
the signal to ground when the FET is turned on.
Fig.7. A silent
applications.
R1
4
10k
D1
OUTPUT
series
0-O OFF
switch
for audio
MATCHED DIODES
D2
INPUT
+12V
OUTPUT
D4
D3
A
OV
B
OV
10k
r--
-12V
R2
INPUT
OUTPUT
12V
----o
--
Q
Fig.6. This series/shunt switch combines
the advantages of the two circuits shown.
above.
ON
ETI APRIL 1980
OFF
OFF
ON
Fig.8. The diode ring switch can operate at very fast speeds.
19
,
CONTROL
HIGH = ON
LOW = OFF
Ring An Ode
The diode ring switch (Fig. 8) is very simple in concept and can
be operated at very fast speeds. When A and B are both at O V no
signal can pass through the ring switch because there is always a
reverse biased diode in the route. When A is +ve and B -Ve (both
with same amplitude), then the 4 diodes are all conducting. Any
voltage at the input of this bridge will cause the same voltage to
appear at the output.
Q OUT/IN
IN/OUT
Vdcl
14
2
13
3
12
4
11
5
10
6
9
Switch In Packs
Fig.9a. The CMOS analogue transmission gate
(top) with 4016 and
4066 pin -outs (left).
I
CONTROL
1
IN/OUT
Vss
I-- OUT/IN
-
8
CIRCUIT
SYMBOL
PIN OUT FOR THE 4016 AND 4066
QUAD TRANSMISSION GATE IC
It is now possible to buy a wide variety of integrated circuits that
perform analogue switch functions. There are perhaps over a hundred different types available, many of which are JFET configurations. These are usually rather expensive and shall only discuss the
more common (and relatively inexpensive) CMOS devices. The
CMOS analogue transmission gate (Fig. 9) is a bidirectional switch
element, having a relatively low on resistance of a few hundred
ohms and a high off resistance.
The input and output terminals can float anywhere in between
the power supply rails and the control input has a high input
impedance. A high (logic 1) connected to the control input turns the
switch on. To avoid distortion problems, the supply voltage should
be kept as high as possible (10 to 15 V) and the load on the output
above 10k. There are two commonly available analogue gate IC's,
the 4016 and the 4066. These are both quad devices with the same
pin -out, the 4066 has the lower Rohl resistance, typically about
* THE INPUT VOLTAGE MUST NOT EXCEED THE PUWEH
SUPPLY VOLTAGE LEVELS OF THE 4016
100R.
Gain Code
The 4016 is a very versatile electronic building block. It can be
used to construct a simple multiplying DAC (Fig. 9). The gain of the
amplifier is linearly proportional to the size of the 4 bit digital code
and can be programmed to give any one of sixteen gains. A low pass
filter (Fig. 10) can have its break frequency programmed by switching in timing capacitors. When all the gates are OFF, the timing
capacitors are ln. The low pass filter can then be tuned by the dual
gang pot over the range 1.5 kHz to 15 kHz. When gates B and D are
on, the timing capacitor is 11 n and so the frequency range is 150 Hz
to 1.5 kHz. Also, when A and C are on, the timing capacitor is 101n
and so the filter range is 15 Hz to 150 Hz. It is possible to build quite
elaborate filter structures, fourth or even sixth order designs and to
make them programmable with analogue switches.
The analogue switch can be used to modify the parameters of
an integrator (Fig. 11). The integrator slew rate can be programmed
by a combination of RA,B,C and the output may be reset to zero
using gate D, which shorts out the timing capacitor.
INPUT
Fig.9b. The 4016 can
be used to construct a
4 -bit multiplying DAC.
39k
22k
FREQUENCY CONTROL
+Ve
TO 4016
OUTPUT
CONTROL
TERMINALS
1
VIN
* DUAL GANG 100k LIN
WIRE WOUND POTS
OUTPUT
100k
INPUT
dB
1.5KHz
150Hz
15Hz
3
TOOn
10n
Fig.10a. A switched- ange ow pass filter.
20
\
FREQUENCY
RESPONSE
2
\
ALL COMPONENTS 2%TOLERAI'CE
15KHz
RANGE RANGE RANGE
USE
66
OR 40011 6
RANGE
SELECT
1
r
-12dó/OCTAVE
\
FREQUENCY
(LOG)
Fig.10b. The low pass filter frequency response.
ETI APRIL 1980